174 



ANATOMY OF VERTEBRATES. 



86 



trituration, — wliile the advantages of a short intestinal tract are 

 obtained, the cliynie is at the same time prevented from being 

 prematurely expelled by the superaddition of the two coecal bags 

 which communicate with the intestines by orifices that are too 

 small to admit pebbles or undigested seeds, but which allow the 

 chyme to pass in. Here, therefore, it is detained, and chylifica- 

 tion assisted by the secretion of the coecal parietes, and the due 

 proportion of nutriment extracted. 



The large intestine is seldom more than a tenth part of the 

 length of the body, and, except in the Ostrich and Bustard, is 



continued straio:ht from the coeca 

 to the cloaca ; it may therefore 

 be termed the rectum rather than 

 the colon. It is usually A\dder 

 than the small intestine, and its 

 villi are coarser, shorter, and less 

 numerous. The rectum, fig. 86, 

 a, terminates by a valvular cir- 

 cular orifice, h, in a more or less 

 dilated cavity, which is the re- 

 mains of the allantois, and now 

 forms a rudimental urinary blad- 

 der, c, d. The ureters, h, h, and 

 eiferent parts of the generative 

 apparatus,/, g, open into a trans- 

 verse groove at the lower part of the urinary dilatation ; and be- 

 yond this is the external cavity which lodges, as in Keptiles, 

 Marsupials and Monotremes, the anal glands and the exciting 

 oro^ans of o-eneration. The anal follicles in Birds are lodo'ed in 

 a conical glandular cavity, k, which communicates with the pos- 

 terior part of the outer compartment of the cloaca, and has ob- 

 tained from its discoverer the name of Bursa Fahricii. 



§ 149. Liver of Birds. — On the hypothesis of chylification, or 

 on that of the formation of blood-discs, or on that of the pro- 

 duction of grape-sugar in relation to the raising of animal heat, 

 being essential functions of the liver, it might have been expected, 

 since digestion is so much more active and the blood so much 

 more abundant and rich, and the temperature so much higher in 

 Birds than in Reptiles, that the liver Avould be proportionally 

 larger ; but it is not so. ' Carefully ascertained upon delicate 

 balances,' the proportionate Aveight of the liver to the body is the 

 same in a Vulture as in a Tortoise, in an Owl as in a Bull-frog, 

 in a Curlew as in a Corn-snake, in a Turkey as in an i\lligator. 



Cloaca of the Cuiidor. xviit'. 



