Philosophical Anatomy, a department of anatomical science, based on data furnished by descriptive and comparative anatomy, embryology, and histology. It is also called transcendental anatomy, as it seeks a fundamental unity in all the forms of nature, and, in the usual restricted signification of the term, aims to establish a primary plan or archetype of which all skeletons, at least of the vertebrata, are modifications. As early as 1807 Oken made three cranial vertebrae, which he calls those of the ear, jaw, and eye, proceeding from behind forward; the auditory nerves traverse the first, the trifacial the second, and the optic the anterior or third; the petrous bone he considers a sense capsule of the ear; he recognizes the vomer as a fourth rudimentary vertebral body, with the lachrymal bones as laminae or neura-pophyses, and the nasals as spinous processes or neural spines; the palate bones he regards as the ribs of the head anchylosed; the squamous portion of the temporal bone of mammals and the tympanic of birds represent the scapula and ilium of the head; he recognized the. arm, forearm, and hand in different parts of the upper jaw, and the corresponding bones of the posterior limbs in the lower jaw; the clavicles of the head were the pterygoid bones.
In fact, the head was to him a repetition of the whole trunk with all its systems; he even states as a fundamental principle that the whole osseous system is only a repetition of a vertebra. After various modifications suggested by other observers or the results of his own researches, in 1843, in his " Physiophilosophy" (Ray society translation, London, 1847), he pursues his cranial homologies still further, always regarding the head as a repetition of the trunk, a doctrine strenuously combated by Owen and others. His theory is detailed at length in the work just quoted, pp. 318-422. His cranial vertebrae are: 1. The occipital, consisting of the body, two condyles, and crest of this bone; this is also the auditory vertebra, as it encloses the auditory bones, and that part of the en-cephalon which gives off the nerves of hearing. 2. The parietal, consisting of the body of the posterior sphenoid, the greater wings, and the parietal bones; this is also the lingual vertebra, the maxillary and lingual nerves passing through the wings. 3. The frontal, composed of the body of the anterior sphenoid, orbital or lesser wings, and two frontals; this is also the optic vertebra, the optic nerves passing through the orbital plates; it also surrounds the cerebrum. 4. The nasal, consisting of vomer, ethmoid, and two nasal bones, containing the olfactory nerves.
The skull contains, therefore, a vertebra to each sense; the sense of touch is disseminated over the whole body, and its vertebrae are 35, 15 in the neck and chest, 5 in the abdomen, and 15 in the lumbar, sacral, and caudal regions. This system is normal only in the human type, animals being irregular men. He says the pectoral and abdominal muscles are ennobled in the muscles of the face; the mouth is the stomach in the head, the nose the lung, the tongue the end of the intestine converted into muscle, and the salivary glands the liver. - The poet Goethe first suggested to anatomists the idea of representing the mutual relations of the bones by figurative diagrams; he had conceived the idea of the cranial vertebra) as early as 1790, but did not make it public until after Oken's inaugural dissertation in 1807. In his essays on comparative anatomy (1819-'20) he made six vertebrae in the mammalian head, three on the posterior part enclosing the " cerebral treasure" and its delicate subdivisions, and three anterior communicating with the external world; these vertebrae are the occipital, posterior and anterior sphenoid, palatal, upper jaw, and intermaxillary.
Dumeril (Magasin encyclopedique, 1808) showed the analogy of the cranial segments and their muscles to the spinal vertebras and muscles; he regarded the basi-occipital bone as a vertebral body, the condyles as oblique processes, the occipital protuberance as a spinous process, and the mastoid as a transverse process. He considered the body of the sphenoid as perhaps a second vertebral centre, but rather inclined to the opinion that the head consisted of a single huge vertebra, with similar form, use, and muscular attachments as a spinal vertebra. Spix (Cephalogenesis, 1815) adopted the number and composition of the cranial vertebrae of Oken's system, only giving them new names. De Blainville (1816) taught in his lectures that the head consists of a series of consolidated vertebrae, developed in proportion to the nervous system contained within them, with simple appendages (ribs), or compound (jaws, limbs, etc.); this is further developed in his Osteographie (1839) and Histoire des sciences de Vorganisation (1845). Bojanus (Isis, 1818) made four cranial vertebrae, the fourth being the nasal, whose neural arch he determined, and the ribs of the tympanic; he named the vertebrae acoustic, gustatory, optic, and olfactory. - Geoffroy Saint-Hilaire (Annates du museum d'histoire naturelle, 1807, vols, ix. and x.) recognized the homology of the pectoral fins of fishes with the anterior extremities of birds, of the bony apparatus of a sternum and its annexes with these parts in higher vertebrates; he attempted the determination of the cranial bones in the crocodile, dividing them into those of the mouth, nose, eye, ear, and brain, regarding the skull as a kind of house with chambers for the lodgment and protection of the brain and organs of sense, but he did not at that time appear to have had the idea of cranial vertebrae; he showed that the cranium of birds was composed of the same bony pieces as that of man and mammals, recognizing a unity of plan of organic composition in all the vertebrata.
His Philosophie anatomique (2 vols. 8vo, Paris, 1818-'22) developed his ideas on the homologies of the vertebrate skeleton; in the Memoires du museum d'histoire naturelle (vol. ix., 1822, pp. 76-119) he gives his ideas on the structure and typical form of the vertebra, and a representation in fig. 5. In the Annates des sciences naturelles (vol. iii., 1824) he explains in a synoptic table (plate 9) the composition of the bony head of man and vertebrates; he makes seven vertebrae, as follows, from before backward: the labial, nasal, ocular, cerebral, quadrigeminal, auricular, and cerebellar. He studied the homologies of the haemal arches more carefully than his predecessors; he made nine pieces in each vertebra, combining, however, some of the parts of the external or dermal skeleton to which the vertebral theory does not apply; he regarded the branchial arches of fishes as the homologues of the tracheal rings of terrestrial vertebrates. With all his errors, Geoffroy Saint-Hilaire gave a great impetus to the study of philosophical anatomy in France. His most powerful and constant antagonist was Cuvier, who treated with ridicule and contempt this form of German philosophy; these two anatomists carried on their discussions, both by lectures and writings, with all the eagerness and often the bitterness of a partisan spirit; ability and brilliancy were on the side of Cuvier, but truth and the more philosophical treatment of the subject were with Geoffroy Saint-Hilaire. - Carus of Dresden (1828) was the most successful cultivator of philosophical anatomy after Oken; in his Grundziige der vergleichenden Anatomie und Physiologic (translated into French by Jourdan, Brussels, 1838) he gives fair credit, though with slight mention, to French anator mists, and lays great stress upon the researches of Germans in this direction; he says incidentally that philosophic osteology owes nothing to the English and Italians, an assertion since contradicted by the appearance of the works of Richard Owen, who, if any one, may be said to represent the present opinion of the scientific world in matters of philosophical anatomy.
Carus maintains that the same relation exists between the three cranial vertebrae and the three cerebral masses pertaining to the three great sensorial nerves (of hearing, vision, and smell), as between each spinal vertebra and the ganglionic swelling of the cord which it envelops. He gave the name of dermatoskel-eton to that which in solidifying separates an animal from the external elementary substance, air or water; this external elementary substance also penetrates within the animal, requiring a more or less solid limitation internally, in the alimentary and respiratory systems, constituting the splanchnoskeleton; the neuro-skeleton is that which limits and protects the nervous system, being peculiar to the vertebrates, the most perfectly developed, and in proportion to the nervous system. The der-matoskeleton is the first and lowest in the animal kingdom; it appears as horny envelope, shell, scales, osseous plates, and skin; it is increased from without, permanent or deciduous, and reproduced by the coagulation or calcification of the integument.
The splanchnoskeleton is also inferior in rank, cartilaginous, but capable of undergoing bony transformation in the higher animals; tracheal rings, branchial arches, and teeth belong to this skeleton; the neuroskeleton is formed as indicated in the article Bone. He divides the cerebral mass into three portions, cerebellum, cerebrum, and optic lobes between them, with three pairs of ganglia in front; the spinal ganglia, in man, are 30. He constructs the skeleton on geometrical principles, starting from the hollow sphere, double cone, and cylinder; he makes what he calls proto-, deuto-, and trito-verte-brae; the first (ribs) enveloping the body and its viscera in relation with vegetative life; the second (vertebrae) protecting the nervous system; and the third (limbs) becoming the osseous framework which sustains the muscular and locomotive organs. His three principal cranial vertebrae correspond to the three cerebral masses, and are the occipital, centricipital, and sincipital; the three facial vertebrae form the nose and its cartilages, and the three intervertebral he names auditive, optic, and olfactory. But it has been found impossible to explain the vertebrate homologies by his diagram archetype; for this the reader is referred to the work above cited.
In fishes we find the first development of the neuroskeleton, as distinguished from the splanchnic and external skeletons, but at its lowest stage, being cartilaginous or partially osseous; it is of inferior vitality, and the component parts are imperfect in form and number; in this class the sexual organs predominate. In reptiles the neuroskeleton is for the first time bony; the splanchnic skeleton is truly cartilaginous, and the external truly corneous; the abdominal region or the digestive system predominates. In birds the thoracic region or respiratory system predominates, extending even into the cavities of the bones and feathers. In mammals the cranium predominates and the nervous system, the neuroskeleton being the highest developed with a corresponding inferiority of the external and splanchnic skeletons. Carus divided the vertebrae into six portions, and the skeleton generally into this number or its multiples, while Oken adopted the number five. - Meckel did not materially affect the progress of philosophical anatomy, but he confirmed many previous principles and homologies by his minute and accurate descriptions, his knowledge of individual formations, and his history of development. - Prof. Owen has given the greatest extension to the science of philosophical anatomy in various writings and lectures since 1838, among which may be mentioned his various "Hunterian Lectures," "Lectures on Comparative Anatomy," " On the Archetype of the Skeleton," uOn the Nature of Limbs," and " On the Principal Forms of the Skeleton and Teeth;" the last is the most popular, and has been reprinted from "Orr's Circle of Sciences" at Philadelphia (12mo, 1854). As far as the skeleton is concerned, the aim of philosophical anatomy is to discover the original idea which presided at its construction, or the archetype to which all the modifications of the vertebrate series can be referred.
The archetype refers principally to the neuroskeleton, which alone appears to have any typical pattern; besides the other skeletons already defined by Carus, of which good examples (of the derma-toskeleton) may be found in the plates of the sturgeon, crocodile, and armadillo, and the carapace of the tortoise, he mentions a sclero-skeleton, or bones developed in tendons, ligaments, and aponeuroses. His typical vertebra is here given:
In the above figure the names printed in Eo-man letters are the autogenous elements, or those which are ordinarily developed from distinct and independent centres; the names in Italics indicate the processes which are continuations of some of the preceding elements; the latter are the diapophyses or superior transverse processes, and the zygapophyses or oblique articular processes of human anatomy.
The autogenous elements enclose generally foramina which form canals in the vertebral chain; the most constant and extensive canal is that marked n, above the central body, for the lodgment of the spinal cord or neural axis, composed of the laminae hence called neurapo-physes; the second canal, marked h, below the centrum, is more irregular and interrupted, lodging the central vessel and the great trunks of the vascular system, and is formed by the lamellae hence called haemapophyses. On the sides of the centrum, most commonly in the region of the neck, is a canal circumscribed by the pleurapophyses or costal processes, the parapophyses or inferior transverse processes, and the diapophyses or superior transverse processes. Thus a perfect or typical vertebra, such as is found in the thorax of man and most of the higher vertebrates, and in the neck of many birds, with all its elements, presents four canals around a common centre; in the tail of most reptiles and mammals the haemapo-physes are joined to the lower part of the centrum, protecting only the artery and vein; but when the central organ of circulation is placed within it, the haemal arch is largely developed, as in the thorax, where the pleura-pophyses (ribs) are much elongated, and the haemapophyses (costal cartilages) are removed from the centrum and placed on the end of the ribs, the bony circle being completed by the haemal spine or sternum; the neural spine is the equivalent of the superior spinous process.
He shows the fallacy of Cuvier's definition of a vertebra; the latter maintained that vertebrae have a special number of pieces arranged in a definite manner, looking more at their position in the series than at their composition; his prejudices against the vertebral theory led him into many untenable and contradictory statements and definitions. Cuvier divided the bones of the head into cranial and facial, making three annular segments of the former; the anterior comprised the frontal and ethmoid, the middle the parietals and sphenoid, and the posterior the occipital, the temporals being intercalated between the occipital, parietal, and sphenoid; he does not apply this to the lower vertebrates, in which it is most evident, nor to the face, or he would have found that these divisions do not include the same bones in all animals, the same being in one a cranial and in another a facial element; this again involved him in many inaccuracies and contradictions. Owen divides the endoskeleton of the human head into four segments, as follows, beginning behind: 1. Occipital or epencephalic vertebra, with the following composition: centrum (c), the basi-occipital portion of the occipital bone; parapophyses (p.) and neurapo-physes (n.), coalesced in the lateral or condyloid portions, the former marked by the ridge for the rectus lateralis muscle; neural spine (n. s.), the proper occipital bone; pleura-pophyses (pl.), the scapulae; diverging appendages (d. a.), the bones of the upper extremity; haemapophyses (h.), the coracoid processes of the scapulae; and haemal spine (h. s.) deficient.
The clavicle and first segment of the sternum, which complete the mammalian scapular arch, are the haemapophyses and haemal spine of the atlas or first cervical vertebra. 2. The parietal or mesencephalic, with c, the basi-sphenoid or posterior part of the body; p., mastoid processes; n., greater wings of spheroid; n. s., parietal bones; pl., styloid processes; d. a., greater cornua of hyoid bone; h., lesser cornua; and h. s., body of hyoid. 3. Frontal or prosencephalic, with c, anterior body of sphenoid; p., external angular processes of frontal (post-frontals of fishes); n., lesser wings of sphenoid; n. s., frontal bone; pi., tympanic portion of temporal; d. a., deficient; h., articular portion of lower jaw; and h. s., dental portion of same. 4. Nasal or rhinen-cephalic, with c, vomer; n., ossaplana of ethmoid; n. s., nasal bones; pl., palate bones; d. a., pterygoid and malar bones, with squamous and zygomatic portions of temporal; h., superior maxillary bones; and h. s., intermaxillaries. The splanchnoskeleton of the head consists of the petrosal and ear bones, the turbinated bones, and the teeth; the external skeleton consists of the lachrymal bones.
These four cranial vertebrae, according to the organs of sense, would be: 1, auditory, related to the organ of hearing; 2, gustatory, with the organ of taste, whose nerve (gustatory or trifacial) pierces the neural arches of this segment or passes between it and the frontal; 3, optic, with the organ of vision between this and the nasal segment; and 4, olfactory, with the organ of smell always in front. Agassiz, in the first volume of his Poissons fossiles, arguing from the fact that the cephalic extension of the chorda dorsalis is arrested in the embryo fish at the region of the greater sphenoidal wings, maintained the "existence of only one cranial vertebra, the occipital, the rest of the head remaining foreign to the vertebral system;" this is refuted by Owen. Owen also combats the idea of Oken that the head is a repetition of the whole trunk; he maintains that" the jaws are not the limbs of the head, but are the modified haemal arches of the two anterior segments; the anterior limbs are diverging appendages of the occipital segment, and the posterior of the pelvic segment with its haemal arch, both variously displaced from their haemal arches in different vertebrates.
The diverging appendages of the ribs of fishes, reptiles, and birds, arising from their posterior edge, are essentially limbs, rudimentary arms and legs, though they never become such. As the cranial segments are in number according to the cranial nerves of sense, so the development of the vertebral bodies and neural arches in the trunk depends on the junction of the nerves with the spinal cord; the condyloid foramen of the occipital bone gives passage in man to the hypoglossal nerve. The cranial bones of fishes are exceedingly complicated, and have taxed the ingenuity of most comparative anatomists, and tried to the utmost the patience of their readers; in his " Comparative Anatomy of Fishes " and " Homologies of the Vertebrate Skeleton," Owen labors very hard, and not always very satisfactorily, to reduce everything to his archetype. It will be interesting and instructive to give a few of the most striking characters of the skeletons of the different classes of vertebrates, according to Owen. In the fish not only the jaws, but the arms and legs, may belong to the skull, which accordingly is developed out of proportion to the rest of the body; the diverging appendages of the frontal vertebra are the chain of opercular bones, and of the parietal the branchiostegal rays; of the first spinal vertebra the pleurapophysis is short and simple, and the haemapophysis is the clavicle; in the abdominal segments the pleurapophyses support simple rays as diverging appendages, and the haemal arches are fibrous; the haemapophysis of the pelvic segment is ossified into an ischium sustaining the ventral fins or posterior limbs, in some instances united to a rib; this pelvic arch is most remarkably changed in position, being as above mentioned in the so-called abdominal fishes (like the salmon, herring, and pike), or joined to the scapular arch as in the thoracic fishes (like the cod and perch families), according as the ischium is joined to the coracoid by a longer or shorter development.
The bony and fibrous parts of the haemal arches contract rapidly beyond the abdomen; the parapophyses increase gradually, curve downward, and complete the arch as in the cod, .or the pleurapophyses contribute to form it with them as in lepidosteus, or the arch is closed by the former, with the latter anchylosed below and diverging at the points, as in the tunny. The bodies of some of the terminal segments in typical osseous fishes are consolidated together, and support several neural and haemal arches and spines, which form the more or less expanded base of the caudal fin. The dorsal, anal, and caudal fins are folds of the skin supported on spines between the neural and haemal spines to which the fin rays are articulated; they form no part of the typical vertebrate skeleton, and are peculiar to fishes. As compared to his archetype figure, the fish skeleton departs from it in the excess of development, principally in the diverging appendages of the cranium, and in the arrest of development in most of the other segments; the principle of repetition predominates, and the segments resemble each other more than in the higher classes.
In the reptile skeleton, the haemal arches of the anterior two cranial vertebrae, the jaws, are more developed, while that of the parietal is feebly so, and they are more or less displaced backward; in the occipital segment the haemal or scapular arch is still further displaced backward and entirely separated; to it is attached an additional single bone, the humerus, and the divisions of the terminal segments are reduced to five, a number not surpassed in any of the higher vertebrates. A part of the body of the atlas is developed separately, and is united to the second cervical vertebra, forming the odontoid process; the nine segments after the cranium are cervical vertebrae, movably articulated, the haemal arches not being ossified, and the pleurapophyses feebly developed, but free or floating; the nine to twelve following are dorsal vertebrae, the elongated ribs with the haemal arch completing the circle, the pieces of which are movable; the next three are the lumbar, without free and bony ribs, but with haemal arches; the next two, united, form the sacrum, bearing the pelvic arch, consisting of pleurapophyses (ilium), haemapophyses (ischium and pubis), with the divergent appendages of the posterior limbs, a higher development than in fishes; beyond the sacrum all the vertebrae are caudal, in which the pleurapophyses become gradually shorter, a few of the first attached to diapophyses, and the haemapophyses articulated between and to two vertebral bodies.
In this class we see for the first time regions of the body. In the bird skeleton the premaxillary is much more developed than the maxillary, the reverse of what is seen in reptiles; the greater volume of the brain requires an increased cranial cavity, which is obtained by the expansion of the neural arches and spines without the addition of-any new bones; the cervical segments have short and free pleurapophyses or ribs, which are early united to the neural arches, forming numerous simple vertebrae, and giving length and flexibility to the neck; the detached haemapophyses of the atlas are usually joined at their extremities, forming a thin osseous arch, the furcular bone; in the thorax the latter are ossified into sternal ribs, the pleurapophyses being the vertebral ribs, bearing diverging appendages, pointing backward, which serve to unite the ribs and to render the thorax more solid; the haemal spines of the anterior thoracic segments are developed into the broad sternum characteristic of birds, with its keel on the median line large in proportion to the powers of flight.
The sacral region is greatly developed, both in the extent and in the number of bones firmly united to form it, and in its enormous pleurapophyses, especially the ilium; the sacrum includes some of the last dorsal, the lumbar, the sacral, and even some of the caudal vertebrae as limited in the reptile skeleton; after the sacrum come five or six caudal, more or less united, the last compressed laterally. and directed upward. The pelvis has only two haemapophyses, the pubis and the ischium, not united on the median line, except in the ostrich for the former and the nandou (rhea) for the latter, the rule being that the pelvis of birds is open below. The diverging appendages of the scapular and pelvic arches, or the anterior and posterior limbs, agree in having only two bones in the carpus and tarsus, and three united in the metacarpus and metatarsus, supporting in the former the second, third, and fourth phalanges, that of the second very rudimentary; in the metatarsus the three bones are, except in the penguins, united for their whole length, including also the two tarsal bones; the rudimentary metatarsal of the great toe is not anchylosed, and is directed backward, supporting the hind toe with two phalanges; the second toe has three phalanges, the third four, the fourth five, the fifth or little toe being wanting; by the number of phalanges we know that, in the African ostrich, the external or shortest toe of the two by its five joints is the fourth, and the internal the third, longer than the other, though having only four joints.
In the mammal skeleton the cranial cavity is expanded, as in birds, chiefly at the expense of the neural spines, frontal, parietal, and occipital; but in most cases the squamous portion of the temporal bone forms part of the cranial walls; the occipital is articulated to the atlas by zygapophyses or condyles developed from the neural arches, and the haemal or scapular arch is generally far removed from the skull; the haemapophyses of the atlas, or clavicles, vary much in extent, in degree of ossification, and even in their presence; the pleurapophyses of the cervical vertebrae are very short, and are generally united to the other elements, circumscribing the foramen for the vertebral artery. The number of the cervicals is seven, except the alleged six in the manatee and the eight or nine in the three-toed sloth; this number depends on the existence of the diaphragm, etc, determining the number and distribution of the pairs of cervical nerves; in some whales and armadillos they are more or less consolidated.
In the dorsals the pleurapophyses or ribs are movable, and the anterior ones are articulated between two vertebras; the haemapophyses are the costal cartilages, and the haemal spines are generally a distinct chain of bones, in the highest consolidated into a sternum; toward the loins the pleurapophyses become shorter, and are attached to their respective vertebral centres and to the diapophyses; the haemapophyses become shorter, and finally free and floating. The caudals vary much in number, size, and form; the short pleurapophyses in the anterior ones are developed at the end of diapophyses, and the haemal arch, when it exists, is articulated directly to the bodies. The limbs (except in cetaceans, where the posterior are wanting) are much alike, whether adapted for flying, digging, swimming, running, or climbing, as will be seen under the homotypes below. In the fish and reptile the vertebral column is straight or nearly so; in the bird the skull forms a right angle with the neck, the latter having a sigmoid curve, and the tail bent upward; in the springing mammals, like the carnivora, there is a convergence of the spinous processes toward the eleventh dorsal, and in most there is a similar convergence toward the fourth cervical, these two regions being the centres of special movements of the column; in bulky animals, like the elephant, which move with a rigid spine, these processes are all inclined a little backward, as in croco-dilians. In man the spine has several slight and graceful curves, destined to prevent shocks to the nervous system from movements incidental to the erect position; the curvature of the sacrum and of the coccyx are greatest compared with the number of vertebrae, and the anterior and posterior diverging appendages reach the maximum of development, especially the latter as compared to the length of the spine; the thumb, which is the least constant part in the rest of the class, becomes in him the most important, constituting a hand proper; in like manner the great toe, the first obliterated in other mammals, is- characteristic of the genus homo, as on it depend principally the erect posture and biped gait of man; even the highest monkey has a posterior thumb instead of a great toe.
In the class of serial homologies, or homotypes, may be mentioned the homology of the scapula with the ilium, the humerus with the femur, the ulna with the fibula, radius with tibia, carpus with tarsus, metacarpus with metatarsus, fingers with toes; in the skull, the basi - occipital, basi - sphenoid, pre-sphenoid, and vomer are the homotypes of the vertebral bodies; the coracoid, superior maxillary, clavicle, pubis, ischium, chevron bones, sternal or abdominal ribs and cartilages, and tendinous intersections of the rectus abdominis, are all homotypes and haemapophyses. This system of homotypes is far more natural, satisfactory, and intelligible than that of Oken, Spix, and Carus, who speak of the scapula, ilium, femur, humerus, etc, of the head, regarding each part as a repetition of the whole. - This is a fair representation of the principal points of philosophical anatomy, as given in the writings of Owen; in many points it is very unsatisfactory, and he labors very hard oftentimes to make out his homologies and to. refer them to his archetype.
With such sources of error and room for variation, it would be useless to expect perfect agreement among authors; from the nature of adaptive organization, it must be difficult if not impossible to reduce skeletons and their parts to unexceptionable laws; organic systems will not be bound down to any such narrow and clearly defined rules, and are constantly presenting to naturalists instances of inexplicable departure from what have long been considered natural laws. Philosophical anatomy will probably always be an uncertain and ever changing study, assisting but not constituting the science of anatomy. Admitting the four cranial vertebras of Oken and Owen, there may still be recognized with equal propriety other vertebral centres in advance of the vomer, analogous to the coccyx at the other end of the column, with no nerves belonging to them. The reason for making four cranial vertebrae seems to have been, both with Oken and with Owen, the existence of four organs of sense in the head, auditory, gustatory, optic, and olfactory; on this principle there would seem more reason for the admission of only three.
In the first place, there are three cerebral vesicles, corresponding to what become cerebellum, optic lobes, and cerebral hemispheres, or according to some anatomists the medulla oblongata may be substituted for the cerebellum; in the next place, there are only three special senses in the head, hearing, seeing, and smelling, taste being a compound sense, made up of smell and touch; the flavor of substances we get from the sense of smell, as the result of a common cold in the head or of artificially preventing the entrance of air by holding the nose sufficiently shows; the rest of the sense of taste is a delicate modification of the sense of touch, placed for protective purposes at the commencement of the alimentary canal; it is absent in many of the lower vertebrates, and has no more claim to be reckoned among the special senses than similar modifications of the sense of touch in the wing of the bat or in the genital mucous membrane; the origin, development, and mode of distribution of the gustatory nerve, which is only a branch of the fifth pair, moreover, are not such as belong to special sense organs. There are also only three sense capsules in the head, the petrous portion of the temporal bone, the sclerotic in the eye (as in the tunny), and the ethmoid for the sense of smell.
As each vertebra of the trunk corresponds to a spinal nerve, there ought to be, according to the view here maintained, three pairs of nerves in the head; excluding the three special sense nerves, the first pair of cranial nerves would be made up of the motores oculorum, pathetic, external motor of eye, and the facial (or the third, fourth, sixth, and seventh) for the motor portion, and the fifth or trifacial for the sensitive portion; the second pair of cranial nerves has the glossopharyngeal and spinal accessory for its motor portion and the par vagum for the sensitive; the third pair of cranial nerves is the hypoglossal, which, though all motor in man, in reptiles (frogs) has the sensory ganglion of an ordinary spinal nerve; in the same manner in reptiles the seventh is seen to belong to the first, and the glosso-pharyngeal and spinal accessory to the second series. We have, then, three cerebral vesicles, three special senses, three sense capsules, and three pairs of craniospinal nerves, which would.seem to indicate three cranial vertebrae, with a rudimentary nasal or other vertebral bodies in front, without nerves belonging to them, corresponding to the coccyx posteriorly.
There is no regularity in the manner in which the nerves, both spinal and cranial, come out of the vertebral canal; the second cranial nerve comes out at the jugular foramen, between the occipital and parietal vertebrae; some of the nerves of the first pair make their exit from the cranium by the foramina rotundum and ovale, and some by the sphenoidal fissure, that is, both through the second and between the first and second; in the human spine the nerves come out between the vertebrae, but in the dorsals of many mammals they pierce the middle of each vertebra. As to the haemal arches, Prof. Owen finds it very difficult so to divide his tympanic series as to get the hyoid arch and lower jaw as appendages to the second and third vertebrae; there is considerable doubt as to whether the diverging appendages of the cranial vertebrae are as yet properly determined. Admitting three cranial vertebrae, with a rudimentary fourth or nasal centrum, let the occipital segment claim the scapular arch; the lower jaw may be appended to the parietal and the upper jaw to the frontal segment, the hyoid arch, as Carus and others maintain, being placed with the tracheal rings in the splanchnoskeleton; or, leaving the hyoid arch in the endoskeleton (which is probably more correct), and pertaining to the parietal segment, the upper and lower jaws may be made the double haemapophy-sial appendages to a single rib, as the ischium and pubis are to the ilium.
There are some facts favoring the latter view, such as the development of both jaws from a single arch; in the cyclostome fishes the mouth is an arch, in which it is hard to say which part constitutes the upper and which the lower jaw; in myx-ine there is no under jaw, the inferior portion of the mouth being made up of the anterior part of the tongue bone. - Closely interwoven with embryology, philosophical anatomy, and zoological classification, is the idea first enunciated by Carus, and afterward extensively developed by Prof. J. D. Dana, that in the higher groups of animals the more important parts of the structure are centralized in the head - called by Dana cephalization. He first applied this idea as a principle of classification in his "Report on the Crustacea of the Exploring Expedition " in 1852; he afterward very fully explained his system in the " American Journal of Science " for 1856,1858,1863, 1864, and 1866, inventing a great number of new terms which cannot be introduced here; those interested can consult the above mentioned volumes.
The fundamental idea is the higher centralization or cephalization of the superior grades of animals, and the less concentrated central forces of the inferior; in the higher groups the centralization contributes to the head functions, or those of the senses and the mouth; as we descend in the animal scale, the head loses one part after another for purposes of locomotion. This cephalization is manifested in the nervous system and in the members of the body. Intimately connected with this is the element of size, which is an important one in animal structure; in the Crustacea, especially, diminution of size generally accompanies a departure from the centralization of the organs in the head, and the increased development of the thoracic and abdominal regions. The same relation of cephalic predominance is as apparent in the embryological development of an individual animal as in the comparative rank in the various groups. In ordinary mammals both the anterior and posterior limbs are organs of locomotion, but in man the anterior are transferred to the cephalic series, serving the purposes of the head; the cephalization of the body, therefore, in him reaches the extreme limit, justifying his elevation by Owen in a group by himself, the archencephala.
Dana maintains that cephalization is a fundamental principle, as respects grade, in zoological life, and throws great light upon classification. The term decephalization he applies to the opposite or descending gradation, in which members are transferred from the cephalic to the locomotive series, with elongation of the thorax and abdomen.. Prof. E. S. Morse, in the "American Journal of Science" for 1866, applies this system to the classification of mollusks. - Though Owen's conclusions are accepted by most anatomists as coming nearest the truth, Mr. Maclise, in the article " Skeleton " of the " Cyclopaedia of Anatomy and Physiology" (vol. iv., London, 1852), looks at the osseous framework from another point of view, and comes to very different results, at only a few of which can we glance here. He denies that there is any such ens as a typical vertebra, and maintains that vertebras are unequal quantities, varying in different regions of the trunk; according to him, the cervical, lumbar, and sacral vertebras develop costal appendages as well as the dorsal; the first seven thoracic costo-vertebral figures are complete, and all other parts of the mammalian spinal axis are more or less modified from this archetype.
The fore limbs are homologous to one another and to the posterior limbs; the scapula and ilium are the homologues of the posterior lamime of a dorsal vertebra, the acromion and inferior iliac spinous processes correspond to transverse processes, and the head of the humerus and femur to the head of a rib. - In 1864 Prof. Huxley instituted a new comparison of limbs, placing them in the position they assume in the embryo, but adopting the view generally maintained in Europe, that their relation is one of parallelism and not of symmetry, or that homologous parts look in the same direction. The opposite view, that of symmetry, or that homologous parts look in opposite directions, has been extensively adopted by American anatomists, and notably by Jeffries Wyman and Dr. Wilder. Prof. Wyman, in a paper on "Symmetry and Homology in Limbs" (" Proceedings of Boston Society of Natural History," vol. xi., 1867), maintains that the fore and hind limbs are not parallel repetitions of each other, like two ribs on the same side of the body, but are symmetrical parts repeating each other in a reversed manner from before backward, as right and left parts do from side to side. He drew attention to the remarkable analogy between symmetry and polarity, thus explaining both normal and abnormal development.
He holds that the two ends of the body repeat each other, without meaning thereby that the head and pelvis repeat each other, as Oken maintained. He denies that the scapular arch is a modified rib belonging to the occipital vertebra, and believes that limbs are not dependencies of the scapular and pelvic arches, but belong to the category of tegumentary organs, their connection with the vertebral column being secondary, like that of the teeth with the jaws. In opposition to the views of Owen, he regards the radius as homologous with the fibula, and the ulna with the tibia. Prof. B. G. Wilder, in his papers on " Inter-membral Homologies," in the " Proceedings of the Boston Society of Natural History," vol. xiv., 1871, and of the "American Association for the Advancement of Science," 1873, combats the old idea of parallelism of limbs, or that the thumb is the homologue of the great toe, etc, and substitutes that of symmetry, maintaining with Prof. Wyman that the above example is simply one of analogy, and that the true homologue of the thumb is the little toe.
He has coined many new and expressive words, his " tools of thought," for the study of the nature and homologies of limbs; he seeks to prove that the cephalic and caudal regions are comparable with each other as are the right and left sides; that the anterior and posterior limbs are appendages respectively of these regions; and that an anterior limb is comparable with a posterior, as the two anterior or the two posterior are comparable with each other. He gives a bibliography of the subject of philosophical anatomy, to which the reader is referred for the views of writers, both European and American, which cannot be alluded to here.