404 ORGANS OF DIGESTION. 



with the cloaca ; their duplicity is analogous to that ob- 

 served in the crop of pigeons, and they are found double 

 also in the hyrax and others among the lower mamma- 

 lia. The cceca-coli are least developed in the grallatores 

 and the nocturnal rapacious birds (129. B. k. h.), where 

 they generally form two small projections on the side of 

 the commencement of the colon. One of these only is 

 developed in the herons, and in several birds, as in the 

 lower vertebrated and invertebrated classes, and as in the 

 plantigrade carnivorous mammalia, there is no coecum-coli, 

 especially among the zygodactylous birds. 



The great intestine terminates in the dilatable rectal vestibule 

 (l29.C.b.D.b.), which is capable of being protruded externally 

 through the cloaca and the anus. The distinction of the cloacal 

 parts of the alimentary canal is most apparent in the ostrich 

 (129. D.), where the rectum (D. a.) expands below into a 

 dilatable vestibule (D. b.) which opens into the upper and 

 back part of the cloaca (D. c.) This upper or first portion 

 of the cloaca corresponds in birds with that which deve- 

 lopes the urinary bladder and allantois in mammalia ; and 

 in the ostrich it serves for the retention of the urine as in 

 the higher viviparous animals. At the lower and back part 

 of this urinal portion of the cloaca, and separated from it 

 by a slight ridge, are the papillar openings (D. /../.) of the 

 two ureters (D. f.' f.'), and exterior to these are the open- 

 ings of the perforate (D. g. gJ) and impervious (D. h.) ovi- 

 ducts in the female, and of the vasa deferentia in the male. 

 To this urethro-sexual canal (D. d.) which receives the ends 

 of the urinary and genital organs, succeeds the preputial 

 cavity (D. e.), the most exterior and posterior portion of the 

 cloaca, which protects the organs of excitement in both 

 sexes, the clitoris (D. k.) of the female and the penis of the 

 male. These terminal parts of the digestive canal are per- 

 ceptible in a less developed form in most other birds, and 

 are represented in Fig. 129. C. as I found them in the fe- 

 male condor vulture, where the separation of the several 

 portions is less distinctly marked. The wide rectum (C. a.) 

 expands below into the rectal vestibule (C. b.}, the highly 

 vascular mucous coat of which differs much in appearance 

 from that of the urinal portion (C. c.) of the cloaca, and is 

 separated from the latter by a distinct circular ridge. The 



