48 VENOMOUS SNAKES AND THE PHENOMENA OF THEIR VENOMS 



a typical mucus-epithelium and a granulated cell, but considered them to 

 be identical only in different stages of function. They considered the gland 

 in the corner of the mouth not identical with the parotis of the mammalian, 

 and named it glandula angularis oris. Cholodokowsky (1892, 1893) declared 

 that the salivary glands of the birds are purely mucus-secreting. Wieders- 

 heim (1898) hesitated to conclude the identity of the gland of the mouth 

 corner of birds with the posterior supralabial gland or the poison gland of 

 snakes, while Gadow (1879) recorded the occurrence of the parotids in 

 various species of birds. As mentioned before, snakes possess the supra- 

 labial glands throughout all families. It was also remarked that only certain 

 snakes have well-developed poison glands. The question may be asked 

 whether the poison gland may be phylogenetically related to the parotid of the 

 mammalia or the glandula angularis oris of the birds. What relation has it 

 to the supralabial glands in general ? The situation and the serous character 

 of the secretion and the single excretory duct of the poison gland suggest 

 strongly a possible homology with the mammalian parotid. The histological 

 and the anatomical examinations of the supralabial glands of many innocuous 

 snakes brought out certain interesting facts which seem to help to trace back 

 the origin of the poison gland. The accounts of the anatomical studies of 

 various glands of the oral cavity by the early investigators are mostly macro- 

 scopic. Meckel (1826) stated that the non-poisonous snakes possess far 

 larger salivary glands than the poisonous ones. A similar finding is in 

 Stannius's work (1846). The supralabial gland (glandula labialis supe- 

 rior, Leydig; glandula maxillaris superior, Oppel) has been exhaustively 

 examined by Tiedemann (1813), Meckel (1826), Cuvier (1810), Cloquet 

 (1821), Duges (1827), Duvernoy (1832), Schlegel (1837), and Leydig (1873). 

 Leydig made the important discovery that the glandula labialis superior of 

 non-poisonous snakes is composed of two distinct parts. The anterior part 

 is reddish-gray in color and consists of many minute glandular grains, with 

 numerous excretory ducts. The posterior part appears yellowish-white and 

 is of coarser glandular grains. It possesses only one excretory duct and is 

 homologized with the poison gland of the venomous species. Reichel (1882) 

 demonstrated an exactly similar condition of the gland with Tropidonotus 

 natrix, one of the harmless, solid-toothed colubrine snakes. 



According to Leydig (1873) the poison gland is not a proper gland, but a 

 modification of one of the lobes of the supralabial gland, and may be present 

 in non-poisonous snakes. It may be here stated that, prior to Leydig, Meckel 

 (1826) announced that the poison gland originates in an enlargement and 

 development of the yellowish portion of the supralabial gland. As early as 

 1833 Duvernoy demonstrated the occurrence of the poisonous gland in many 

 species hitherto considered non-poisonous, and declared thereby that the 

 simultaneous presence of the poison fang is one of the essential characteristics 

 of the poisonous snakes. Phisalix and Bertrand (1894) look upon the toxic 

 property of the adder blood as deriving from the supralabial gland through 

 the internal secretion, and the natural immunity of the same animal against 

 the viperine venom as the result of constant immunization by the same prin- 



