266 NATURE-STUDY REVIEW [12:6-Sept., 1916 



Viperidae is divided into two sub-families, these technically termed 

 the Viperinae (the True Vipers), the species of which are found 

 only in the Old World, and the Crotalinae. or 'Pit Vipers', occur- 

 ring in both the Old and the New World, but attaining their great- 

 est size and variability of form in the latter. Thus, in North Am- 

 erica, all of the thick-bodied poisonous snakes are ' Pit Vipers' or 

 Crotaline serpents. The members of both sub-families may be 

 recognized by the flat triangular head, very distinct from the neck 

 and the elliptical (cat-like) pupil of the eye. The top of the head, 

 with the majority of the species, is covered with very small, gran- 

 ular scales. Some show regularly arranged head shields of much 

 the same formation and character as those of the colubrine snakes. 



'The sub-family Crotalinae, containing the copperhead, the 

 rattlesnakes, the moccasin and the 'fer-de-lance' has acquired the 

 popular .title for its members — the Pit Vipers — owing to a peculiar 

 development seen with all the species. This consists of a deep pit, 

 situated between the eye and the nostril. The orifice is lined with 

 a delicate epidermis and connects with a well-developed nerve ex- 

 tending backward to the brain. That this pit is of some use to the 

 snake, seems very probable, when the attendant nerve develop- 

 ment is considered. Many investigations have been attempted, 

 with the result of complicated anatomical repetitions in the line 

 of description, but with no actual proof of the function of this 

 organ. 



Mr. Ditmars led the writer from cage to cage pointing out the 

 pit in the heads of the various snakes ; it is readily to be seen and 

 forms a valuable identification mark. Speaking of the poison 

 apparatus of the Crotaline snakes, he said "It consists of two 

 long and hollow teeth — the fangs — provided with an elongated 

 orifice at their tips for the ejection of the venom. These fangs 

 are the exact reproduction, in hard enamel, of the hypodermic 

 needle. It might be more appropriate to say that the needle was 

 patterned from the fangs. The fangs are rigidly fastened to a 

 movable bone of. the upper jaw, and each connects with a gland, 

 situated behind the eye, and containing the venom. When the 

 mouth is closed, the fangs fold back against the roof of the mouth. 

 As the jaws are opened, they spring forward, ready for action. 

 The forcible ejection of venom from the fangs is caused by the con- 

 traction against the gland, of the muscles which close the jaws. 

 The ejection of poison is voluntary, and unless the reptile so de- 



