AVES BIRDS. 615 



scribed when speaking of the ear of Reptiles ( 639, 640), as to 

 render repetition needless. A single trumpet-shaped bone, the 

 representative of the stapes, fig. 281. 



communicates immediately 

 between the mem bran a tym- 

 pani and iliefenestra ovalis ; 

 but two or three minute car- 

 tilaginous appendages, con- 

 nected with the membranous 

 drum of the ear, are regard- 

 ed as being the rudiments of 

 the malleus, incus, and os 

 orbiculare met with in the 

 next class. 



(685.) The kidneys in the Bird (Jig. 282, e, e, e) 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. 



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 pas- 

 sages : 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 ; they are, moreover, 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 (Jig. 282, TO, m) contains the orifices of the ureters and genera- 

 tive canals ; the latter is, therefore, generally distinguished by the 

 name of urethro-sexual portion of the cloaca, and is in truth a 

 remnant of the allantois, and a rudiment of a bladder for the ac- 

 cumulation of the urine. 



(686.) An unctuous secretion, peculiar to the class under 



