60 



VENOMOUS SNAKES AND THE PHENOMENA OF THEIR VENOMS 



gland. Its anatomical position corresponds with that of the parotid gland 

 of the Mammalia, to which its similarity is still further strengthened by the 

 serous character of the secretion. A certain digestive function of the poison 

 gland has been described and is alleged to be essential to digest the prey. 

 The venom gland Hke the parotid gland has only one excretory duct. Allu- 

 sion has been made to the fact that the secretion of the poison gland has a 

 double importance to the reptile — to assist digestion and to capture prey. 



The dimension^ of the poison glands is generally in proportion to the size of 

 the snakes, although some exceptions are observed in certain species. Of 

 the Crotalidse with the length of about 5 feet the gland attains the size of an 

 almond. The cobra is provided with a somewhat larger gland. The Euro- 

 pean vipers have much smaller glands, as their size is not very great. It is 

 a curious fact that the genus Doliophis, one of the venomous colubrine genera, 

 is characterized by the possession of a very large, elongated poison gland 

 which extends down one-third of the entire length of the body. It ends in a 

 club form in front of the heart, shifting the latter to the right. Especially 

 Doliophis 2 intestinalis and Doliophis hivirigatus are noted for their enormous 

 glands. In the visceral region the glands are in one mass and separate from 

 one another near the head in order to supply the poison fang on each side. 

 Similar glands are described by Meyer in Doliophis philippinus, Doliophis 

 nigroicBniatus, and Doliophis flaviceps. 



The gland is surrounded by striated muscle fibers which run parallel to its 

 longitudinal axis. According to Meyer and Hoffmann (1890) another duct 

 opens near the exit from a second large gland which lies behind the eye. In 

 Causiis rhomheatus Reinhardt discovered a poison gland disproportionately 

 large. In a specimen which measured 18 inches the gland with the duct 

 reached 3 inches. The gland runs down along each side and lies on the ribs 

 and muscles, and is provided with a muscle attached to it. 



The poison gland is for the most part a serous gland. A considerable 

 variation is noted in the structure of poison glands throughout Ophidia. In 

 proteroglyphous colubrine snakes the alveoli of the gland are much larger and 

 have a lining epithelium of short columnar cells inclosing a capacious lumen 

 in which secretion is stored. The supporting framework of interalveolar 



1 S. Weir Mitchell gives the following measurements for the Crotalus adamanieus kept two to eight 

 weeks in captivity: 



2 Meyer, the discoverer of this visceral poison gland, used the term Calliophis or Callophis, but Wil- 

 helm Peters (1871) devised a special generic name Adeniophis for this particular group. Bou- 

 lenger again employed the third name Doliophis in lieu of Peters's Adeniophis. 



