HABITS. 363 



carotids.* These may arise from tlie arch by a common stem, 

 and the right is usually smaller than the left. In other snakes 

 only one carotid and that the left is present. In such cases it 

 often happens that there is an artery in place of the right carotid, 

 which goes to the blood-glands in front of the pericardium 

 (a. thyroidea). There are, of course, no subclavians. The left 

 arch gives off no vessels. The anterior abdominal vein is single 

 and arranged as in LacertiUa, i.e. it conveys blood from the 

 ventral body wall and bladder to the liver. The caudal vein is 

 continued as the renal portal. 



The kidneys are elongated, slightly lobed bodies placed at 

 some little distance in front of the cloaca. They are not quite 

 symmetrical the right extending a little further forward than the 

 left. The ureters leave their hind ends and are of some length ; 

 they open through the side-walls of the cloaca on a papilla which 

 in the males contains also the opening of the vas deferens. There 

 is no urinary bladder. 



The genital glands are like the kidneys slightly asym- 

 metrical ; those of the right side reaching a little further forward 

 than the left. The testes are usually rather elongated bodies 

 and lie in front of the kidneys. The coiled vasa deferentia lie 

 along their inner sides and open behind, as stated, into the cloaca 

 close to the ureters. The ovaries are elongated and consist 

 of two lamellae with a lymph space between them. The oviducts 

 have the usual arrangement. The penes are paired evagin- 

 able cloacal pouches and closely resemble those of lizards. 



Accessory glands in the neighbourhood of the anus are found 

 in both sexes of many snakes. 



Most snakes are oviparous, but in a few (many sea-snakes and 

 vipers) the development takes place in the oviduct and the young 

 are born fully developed. The eggs have soft shells and are laid 

 in comparatively small numbers, it may be at an advanced stage 

 of development. The embryo possesses a tooth-like process on 

 its premaxilla for breaking the shell. 



Snakes feed exclusively on living animals, both warm and 

 cold-blooded, which they attack suddenly, and swallow without 

 mastication. Swallowing is effected thus : the teeth on the 

 lower jaw are alternately hooked further and further forwards 

 into the body of the prey (the two halves of the mandible 



* Rathke, Denkscliriften Wiener Akacl. xi, 1856,.Abt. 2, p. 1. 



