PHYLOGENY OF VENOMOUS SNAKES 47 



the poisonous to the non-poisonous species. The question may be raised as 

 to whether the poison gland and fang came into existence at the same time, 

 or whether one antedates the other. If not of simultaneous appearance, 

 which of the two came first ? Through elaborate work of various investiga- 

 tors it was made clear that the poison gland does exist in the group of snakes 

 which possesses no grooved or perforated teeth, and the presence of the 

 grooved tooth is always associated with a much more developed venom gland 

 than the rudimentary form of the aglyphous species. The poison gland of the 

 snake is a modified form of the glandula labialis superior and in all probability 

 is equivalent to, if not identical with, the parotid of the mammalia. 



In the Urodelia and the Anura the oral cavity is provided with the mucus- 

 secreting glands which are located in the internasal and lingual regions, and 

 also in the pharyngeal area in the latter order. In the Chelonia the medial 

 and lateral palatine glands take the place of the internasal, and the sub- 

 lingual appears anew. In the Crocodilia no sublingual gland is present. 

 First in the Sauria, comprising both the Lacertia and the Ophidia, the glan- 

 dula labialis, superior and inferior, are added to the sets already mentioned. 

 For the Ophidia no palatine gland is present, but there is sometimes the 

 poison gland. Phylogenetically considered, the salivary glands appear first 

 in the Amphibia, in which the mucus-secreting glands are the only kind. 

 In the Pisces no salivary gland is found. The majority of the Reptilia 

 possess the mucous gland with a fairly high, clear cylindrical epithelium, 

 which contains more or less granules in the protoplasm (Wiedersheim, 

 1886). In this class, however, not only the number of glands, but also their 

 shape, arrangement and structure, become more abundant and variable, with 

 acquisition of certain new functions at the same time. In certain Sauria, for 

 example, the Lacertia and Anguis fragilis, a serous and a mucous gland are 

 formed in the area of the sublingual gland, a fact which shows that the con- 

 dition is gradually approaching the mammalian class. 



The poison gland of snakes has occupied the minds of many great anato- 

 mists for solution of its origin and its relation to the salivary glands, both in 

 the same order and in the orders next to it. Comparative studies of Carus 

 (1834), Tiedemann (1810), Meckel (1829), Stannius (1846), Ellenberger 

 and Hoffmeister (1881), and others demonstrated that in the mouth of birds 

 of prey there are at least four to five sets of glands, corresponding to the sub- 

 maxillary, sublingual, lingual, parotid, and a group of glands (follicle) near 

 the side of and behind the posterior nostrils, which, together with a large 

 group around the Eustachian tube, was held for the tonsils by Rapp (1843). 

 Rapp's interpretation was shown to be incorrect by the work of Kahlbaum 

 (i8s4),Leydig (1857), Stohr (1884), Gadow (1891). The peculiarity^ the 

 avian mouth is in the presence of a pair of glands over the maxillary joint. 

 Carus (1834) was not able to decide whether it is to be considered an analogue 

 of the parotid of the mammalians or the poison gland of snakes. Ranvier 

 (1884, 1887) held that the cells of the gland erroneously called the'submaxil- 

 laris are mucus-secreting, which is not the case with the gland of the labial 

 commissure. Battelli and Giacomini (1889) described two types of cells, 



