(ESOPHAGUS, STOMACH, AND INTESTINE 339 



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 Amphisbsenians possess a 

 narro\v, 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 other Lizards the 

 coils are more marked, and in forms with broad bodies (e.g. 

 Chelonians, Crocodiles) 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. [For the 

 urinary (allantoic) bladder present in many Reptiles, cf. under 

 Foetal Membranes and Urinary Organs.] 



In many Reptiles (e.g. most Lizards, Snakes), a small blind- 

 gut or caecum is present 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. 250, A). 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. 

 The former, which on account of its richness in glands is called the 

 glandular stomach (proventriculus), alone takes part in dissolving 

 the food; while the latter, which is lined by a keratinoid layer 

 consisting of a hardened glandular secretion, has simply the 

 mechanical function of grinding the food, in correlation with 

 which a very peculiar and thick muscular wall provided with two 

 tendinous discs is developed (Fig. 250, B and c). The degree 

 of development of this muscular stomach, or gizzard, is in 

 direct proportion to the consistency of the food. Gramini- 

 vorous Birds possess the strongest muscular layer and the thickest 

 keratinoid lining, while in the series of insectivorous Birds, up to 

 the Birds of Prey, this condition becomes gradually less marked, 



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

 horny papillae, and in the stomach a differentiation of distinct gland-zones is 

 seen, such as is already indicated in certain Fishes and is carried still further in 

 Mammals. 



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