SERPENTS. 



351 



thus : Many people maintain they have seen the animals pass into the mother's 

 mouth in time of danger ; some fishes, Arii, are known to protect their young by re- 

 taining them in the mouth ; a male amphibian, JRhinoderma darwinii, carries the eggs 

 in a laryngeal pouch until they are well developed ; young serpents could live for 

 some time shut up in the mouth, gullet, or even stomach of their parents ; the 

 belief is an old one and well established. On the other hand, no naturalist of good 

 standing has ever been able to observe the young serpents thus seek safety ; and of 

 the serpents found in the gullet of dissected snakes, all have been of a different 

 species, or immature individuals of the same species as their devourers, and were 

 undoubtedly taken as food. 



The skeleton of ophidians is chiefly axial, there never being any pectoral girdle, 

 and only rarely (in Opoterodonta and a few families of Colubriformia, as the Tortrici- 

 dsB, Pythonidae, and Boidae) a pelvic girdle with rudimentary limbs. When the 

 hind limbs are present, they appear, externally, as two short claws or processes each 

 side of the anus, and are probably used as clasping organs. The two rami of the 

 lower jaw are not united in fi-ont by a bony sym- 

 physis, but by an elastic ligament, giving them 

 considerable lateral expansion with the ordinary 

 vertical movement. The bones of the upper jaw 

 are also so connected with the other bones of the 

 face as to allow more or less individual movement. 

 The teeth are never permanent, but are capable 

 of being renewed, like those of fishes, as soon as 

 the old ones are worthless. They all point back- 

 ward, and those of the palatine and pterygoid 

 bones resemble the armature of the jaws. 



The vertebras are concave in front and convex 

 behind, and connected by free ball and socket 

 joints, twisting being prevented by horizontal 

 articular surfaces ; those of the body seldom exceed 

 three hundred in number. The ribs are the chief 

 organs of locomotion, being attached at their free 

 ends not to a sternum but to the ventral scutes. 



The alimentary system is elongate and adapted 

 to the general form of the body. In the disten- 

 sible mouth the food is subjected to the treatment of saliva, which, in its or- 

 dinary form or as poison, is given off in considerable quantities, and materially aids 

 in the process of digestion. The stomach is a simple enlargement at the end of the 

 oesophagus, provided with longitudinal folds, and in turn leads into a relatively short 

 intestine. The liver is asymmetrical, and passes from the anteriorly placed heart to 

 the pylorus ; its reservoir, the gall bladder, is somewhat removed, and is placed, with 

 the pancreas and spleen, in a fold of the duodenum. Though serpents drink a great 

 deal of water, and will perish if it is not given them, they have been kept for months 

 without nourishment of any kind whatever. 



The respiratory system is peculiarly specialized. The lungs are paired only in the 

 boas, some Proterogylphs, and the Crotalidas, in other forms only one is developed, which 

 may be specialized into an air-sac posteriorly, its fellow appearing only as a rudiment. 

 The trachea is long and may be provided with air-cells, and the larynx can be projected 



Fig. 208.— Skull of snake ( Tropidonotus) ; an, 

 angular ; ao, antorbital ; ar, articular ; d, 

 dentary ; eo, exoccipltal ; /, frontal ; p, 

 parietal ; pi, palatine ; pm, premaxillary ; 

 pr, prootic ; pi, pterygoid ; g, quadrate ; sa, 

 surangular ; sh, stylofiyoid ; so, supraoccipi- 

 tal ; sg, squamosal. 



