262 COMPARATIVE ANATOMY 



of a caecum are seen in certain Teleosts. In the Dipnoi a cloacal 

 caecum is present (Fig. 209). 



In all Fishes in which a cloaca is absent (p. 259) the anus is 

 anterior to the urinogenital aperture. 



Reptiles. In correspondence with the more definitely differen- 

 tiated neck, the oesophagus of Reptiles is relatively longer than in 

 the animals as yet considered; it is always plainly marked off 

 from the much wider stomach, which is usually sac-like, or bent 

 upon itself, in which latter case it lies transversely (Chelonians). 1 

 As regards external form, the stomach of Crocodiles is more 

 specialised than that of other Reptiles, approaching that of Birds. 



Snakes, Snake-like Lizards, and Amphisbaenians possess a 

 narrow, spindle-shaped stomach, which lies in the long axis of the 

 body ; in correspondence with the large size of the masses of food, 

 which are swallowed whole, it is capable of great distension. In 

 these the intestine is only slightly coiled : in Lizards the coils 

 are more marked, and in the other forms, with broad bodies, the 

 folding is carried still further. 



The large intestine has a straight course, is often considerably 

 swollen, and opens into a cloaca. It may (e.g., certain Chelonians) 

 be as long as the small intestine and be bent on itself. An account 

 of the urinary (allantoic) bladder present in many Reptiles will be 

 found in a subsequent chapter. 



From the Reptilia onwards a blind-gut or caecum is usually 

 formed at -the anterior portion of the large intestine : it is 

 generally asymmetrical. 



Birds. In correspondence with the kind of nutriment, the 

 mode of life, and the absence of teeth, certain modifications of the 

 oesophagus and stomach occur in Birds. In graminivorous Birds and 

 Birds of Prey either the whole gullet forms a dilated sac or else it 

 gives rise to a ventral outgrowth ; in both cases the enlargement 

 is known as the crop (inglumes) (Fig. 211). This serves as a food 

 reservoir, and in some cases its walls are glandular. 



The stomach, instead, of remaining simple, generally becomes 

 divided externally into two portions, an anterior and a posterior 

 (Fig. 211). The former, which on account of its richness in glands 

 is called the glandular stomach (proventricuhis\ alone takes part 

 in dissolving the food ; while the latter, which is lined by a horny 

 layer consisting of a hardened glandular secretion, has simply a 

 mechanical function, in correlation with which a peculiar and very 

 thick muscular wall provided with two tedirious discs is developed. 

 The degree of development of this muscular stomach, or gizzard, 

 stands in direct proportion to the consistency of the food. In 



1 The oesophagus of marine Chelonians, 'like that of many Birds, is lined by 

 horny papillae. 



