BRANCH CHORDATA: CLASS REPTILIA 37 



thyroid may be seen a long glandular mass, the tJiymus 

 gland. The functions of these glands are not certainly 

 understood. 



Remove the alimentary canal and muscles from a part 

 of the body and note that the axial skeleton, like that of 

 the other vertebrates studied, consists of a series of verte- 

 bra placed end to end. Are there arms or legs ? Are 

 shoulder and pelvic girdles present ? How many of the 

 vertebrae bear ribs ? The ribs connect at their lower ends 

 with the ventral scales. Note the great number of the 

 vertebrae and ribs as compared with those of the toad or 

 fish. What are those vertebrae called which bear no ap- 

 pendages or ribs ? Examine carefully the elongated skull 

 of the snake, especially the modified jaws. A detailed 

 study of the skeleton may be made by referring to 

 the account of the skeleton of the lizard in Parker's 

 " Zootomy, " pp. 130 ct seq. 



The nervous system may be worked out in a specimen 

 which has been immersed in 20 per cent nitric acid. The 

 description of the nervous system of the toad (see pp. 1 2- 

 13) will suffice for a guide to the study of the nervous 

 system of the snake. The special sense organs, as eyes 

 and ears, should be examined and compared with those 

 of the fish and toad. 



Life-history and habits. The garter snakes are more 

 or less aquatic in habit and are good swimmers. They 

 are often found far from water, but in greatest abundance 

 where the cat-tails and rushes grow thickest. They feed 

 on frogs, salamanders, and field-mice, which they swallow 

 whole. All the garter snakes are ovoviviparous, i.e., 

 hatch eggs within the body-cavity. The eggs, often as 

 many as eighteen or twenty, are enclosed within widened 

 portions of the oviducts during embryonic existence; when 

 the young are born they are able to shift for themselves. 

 During cold weather the garter snake hibernates, hiding 



