This section is from the book "General Outline Of The Organization Of The Animal Kingdom, And Manual Of Comparative Anatomy", by Thomas Rymer Jones. Also available from Amazon: A General Outline of the Animal Kingdom and Manual of Comparative Anatomy.
* Vide Barkow, in Meckel's Archiven, Band xii. 1 Cuvier, Lecons d'Anat. Comp. tom. ii. p. 431.
(2085). Being thus provided with moveable eyelids, a lacrymal apparatus is, of course, indispensable; and accordingly, birds are supplied with two distinct glands, one being appropriated to the secretion of tears, while the other furnishes a lubricating fluid, apparently destined to facilitate the movements of the membrana nictitans.
(2086). The lacrymal gland is situated, as in Man, at the outer angle of the eye, and its duct pours the lacrymal secretion upon the eyeball near the external canthus. The lacrymal canal, whereby the tears, after moistening the cornea, are discharged into the nose, commences by two orifices (fig. 366, a, c) situated just behind the internal commissure of the eyelids, and is continued into the nasal cavity, where it terminates in front of the representative of the middle turbinated bone.
Fig. 366. Muscles of the nictitating membrane.
(2087). The second gland, the glandula Harderi, seems to supply the place of the Meibomian glands of the human eyelids: it forms a considerable glandular mass, situated behind the conjunctiva, at the nasal angle of the eyelids; and through its excretory duct, which opens behind the nictitating membrane, the lubricating secretion that it furnishes is poured out.
(2088). Besides the secreting organs above described, a third very large gland is found, generally lodged in a depression beneath the vault of the orbit, although in some genera it is situated external to that cavity: the secretion of this gland, however, is poured into the nose by one or more ducts, and thus serves copiously to moisten the Schneide-rian membrane.
(2089). The auditory apparatus of a Bird is almost precisely similar in its structure to that of one of the more perfect reptiles, such as the Crocodile. There is still no external ear, or osseous canal worthy of being called an external meatus: yet in a few rare instances, such as the Bustard, the feathers around the ear are so disposed as to collect faint impressions of sound; and in the Owls, besides possessing a broad opercular flap, that forms a kind of external ear, there are sinuosities, external to the membrana tympani, which resemble, not very distantly, those found in the ear of Man.
(2090). Entering into the composition of the organ of hearing in the class before us, we have the membrana tympani (fig. 367, a), and tympanic cavity, from which a wide Eustachian tube (d) leads to the posterior nares. The labyrinth presents the vestibule (c), the semicircular canals (b), and the rudimentary cochlea (e); all of which so exactly correspond in structure with what has already been described when speaking of the ear of Reptiles (§1997 et seqq.), as to render repetition needless. A single trumpet-shaped bone, the representative of the stapes, communicates immediately between the membrana tympani and the fenestra ovalis; but two or three minute cartilaginous appendages, connected with the membranous drum of the ear, are regarded as being the rudiments of the malleus, incus, and os orbiculare met with in the next class.
(2091). The kidneys in the Bird (fig. 368, eee) are very large; they are lodged in deep depressions, situated on each side of the spine, in the lumbar and pelvic regions, their posterior aspects being moulded into all the cavities formed by the bones in that situation. In their essential structure each kidney is made up of innumerable microscopic flexuous tubes, which, joining again and again into larger and still larger trunks, ultimately terminate in the ureter, without the interposition of any infundibular cavity analogous to the pelvis of the human kidney.
Fig. 367. Organ of hearing in the Owl.
Fig. 3G8. Generative organs of the Cock.
(2092). From the manner in which the kidneys are imbedded, the ureters are necessarily derived from their anterior aspect. After receiving all the terminations of the urinary tubules, they pass behind the rectum to the cloaca, into which they discharge the urinary secretion. The cloaca, therefore, receives the terminations of the rectum, of the ureters, and also, as we shall immediately see, of the sexual passages: no urinary bladder is as yet developed, nevertheless vestiges of its appearance begin to become visible. The cloaca is, in fact, in some birds divided into two compartments, distinct both in their appearance and in their office; these, moreover, are separated by a constriction, more or less well-defined in different species. It is into one of these compartments that the rectum opens, while the other (fig. 368, m m) contains the orifices of the ureters and generative canals; the latter is therefore generally distinguished by the name of the ureihro-seooual portion of the cloaca, and is in truth a remnant of the allantois, and a rudiment of a bladder for the accumulation of the urine.
(2093). An unctuous secretion, peculiar to the class under consideration, has been provided for the purpose of oiling the feathers; and in water-birds the fluid alluded to becomes of very great importance to their welfare, as it causes their plumy covering to repel moisture so efficiently that it is never wet. The gland given for this purpose is called the "urojoygium" and is situated upon the back of the os coc-cygis; from this source the bird distributes the oily material thus afforded to all parts of its plumage.
(2094). The male generative organs in Birds are fully as simple in their structure as those of the Reptilia. The testes are two oval bodies (fig. 368, g), invariably situated in the lumbar region, lying upon the anterior portion of the kidney. In their intimate structure they consist of contorted and extremely slender tubes, wherein the semen is elaborated, contained in a strong capsule. The sperm-secreting tubules of each testis terminate in a slightly flexuous vas deferens (h, i), that opens into the cloaca by a simple orifice (m m.) In most birds it can scarcely be said that a penis exists at all, two simple rudimentary vascular papillae at the termination of the vasa deferentia constituting the entire intromittent apparatus; so that copulation between the male and female must, in the generality of species, be effected by a simple juxtaposition of the sexual orifices: nevertheless in the web-footed tribes, which copulate in the water, and in the Ostrich, the penis of the male is much more perfectly organized, as will be seen by the following description extracted from Cuvier*.