Dissected so as to show, superiorly, the cerebrospinal nervous system lodged in the craniospinal cavity, and, inferiorly, portions of most of the organs of Vegetative life.
Plate I. Common Rat, Mus decumanus.
Characters distinctive of Mammalia shown in this figure are the following: the epidermic exo-skeleton in the form of hairs; the suspension of the lungs freely in closed 'pleural' sacs; the perfect diaphragm (c) separating the cavities of the thorax and abdomen; the smooth external surface of the kidney; the single aorta crossing the left bronchus; and the presence of an omentum or epiploon (w).
The scalpriform incisors characteristic of the order Rodentia are concealed in this profile view by the lips, but the figure shows well the great size of the masseter muscle which is crossed by-ihe duct of the parotid gland (j) and by the facial nerve. The great size of the organs of special sense relatively to the entire bulk of the animal, and of the hind limbs relatively to the fore limbs, are characteristic, though not universally nor exclusively, of Rodents.
Points of less classificatory importance are furnished to us by the presence of a vena cava descendens on the left side; of smooth cerebral hemispheres (h); of a uterus all but completely bifid (y and y); of a Har-derian gland (f); of a hibernating gland (k); and of a double lacrymal gland (g and g').
The left halves of the parietes of the craniospinal, thoracic, abdominal, and pelvic cavities have been removed to expose the parts shown in this figure. The integument has been removed from the greater part of the facial region, but a narrow strip has been left connecting the concha of the ear with the upper eyelid. A similar strip has been drawn as left in situ overlying the costal attachment of the diaphragm.
1 Plates I, VI, VIII, and X, are taken from the specimens described in the first part of this work. Plates II, III, XI, XII, and XIII, are from specimens of the same animals as described in the first part, but prepared differently, and therefore often displaying new points. In describing these Plates repetition is avoided as much as possible. Plates IV, V, VII, IX, and XIV, relate to animals or groups not described before. The descriptions of these Plates are therefore supplementary to the descriptions of specimens in the first part.
a. Left eye.
b. Left ear.
c. Diaphragm forming a contractile dome-shaped floor between the abdominal cavity below and the thoracic above.
d. Eleventh dorsal or anticlinal vertebra.
e. Spinal cord. The part where it widens into the medulla oblongata is concealed by the large external ear.
f. Part of Harderian gland, which discharges its secretion by a duct opening under the rudimentary third eyelid or nictitating membrane. This gland is found in most mammals, with the exception of Chirop-tera and Simiadae.
g. Intra-orbital portion of lacrymal gland.
g'. Extra-orbital portion of lacrymal gland, lying upon the masseter muscle. It sends a duct with some glandular tissue inlaid in its walls to enter the orbit at its posterior angle, and receive the duct of the intra-orbital portion (g). h. Cerebral hemisphere of right side. i. Vagina.
j. Parotid gland. Its ducts are seen to converge from its constituent lobules, which are loosely aggregated from the neighbourhood of the ear to that of the acromion, and to cross, when united, the ramifications into which the motor nerve of the facial muscles is seen to break up. The buccal pouch is wanting in the true Mures. Some lymphatic glands have been removed from the space between the masseter muscle and the parotid gland. k. Portion of 'hibernating gland;' a gland found in many Rodentia, Chiroptera, and Insectivora, and spreading in them into the axillary, the nuchal, the thoracic, and even occasionally into the abdominal regions. l. Submaxillary gland and duct, m. Heart; the line ends upon the left ventricle. The apex of the heart is not turned so much to the left as in man and in some of the lower mammals, e.g. the mole. The fold immediately below the point . where the line abuts upon the ventricle is formed by the cut edge of the pericardium. n. Left auricle. \ o. Phrenic nerve.
\ p. Aorta. A bristle has been passed between it and the left azygos vein, and abuts on the diaphragm where the left phrenic nerve enters it. Behind this bristle are seen, passing from the aorta to the sternum, first, the third lobe of the right lung; secondly, the oesophagus; thirdly, the fourth lobe of the right lung within its own pleural cavity, in relation with which is the phrenic nerve; and, lastly, the lobules of fatty tissue, already spoken of, in apposition with the fourth and fifth of the six sternal bones. q. Left azygos vein joining the vena cava superior of the same side, and receiving some veins from the masses of fat just mentioned in connection with the pericardium.
r. Root of left lung: the lung of this side has been removed; it consisted of a single lobe, as is often, though not always, the case in Rodentia, Marsupialia, and Insectivora, though very rarely in Carnivora and Quadrumana; see Cuvier, Lecons d'Anatomie Comparee, torn. vii. ed. 2nde, 1840, pp. 156-163. - s. Kidney.
v. Liver; the line abutting upon its left lobe. w. Omentum or epiploon.
x. Coecum. The entrance of the small intestine into the coecum is not seen, but we observe that the coecum becomes smaller in calibre where it is bent on itself superiorly.
x. Convolutions of intestines.
y. Upper end of left cornu of pregnant uterus, passing into the Fallopian tube, which together with the ovary fills up the space between this convolution of the uterus and the kidney. yr. Lower portion of same uterine cornu distended with foetuses. z. Bladder contracted into a conical shape and receiving the ureter at its base on the left side.
z. Outlet of urinary organs through a perforated clitoris distinct from the vagina.
A. Flexor muscles of the tail, which arise from the internal surface of the pelvic bones.
h. Anterior portion of ilium, the posterior part of which has been removed, together with the pubis and ischium. From its internal surface the caudal flexors are seen to take origin, and in front of them and in a line with the point on which the letter 8 is placed, the cut end of one of the great veins returning blood from the hind limb is seen.