POISON^APPARATUS^OF VENOMOUS SNAKES 61 



La- 

 connective tissue varies in amount in different species, but in all cases it is 



developed to a greater extent in the center of the gland in the region of the 

 forwardly converging ducts. The poison duct, which is longitudinally folded 

 for the greater part of its course, has opening into it, throughout its length, 

 a series of small glands completely surrounding it. These minute lobules 

 are mucous glands and are difficult to stain, and the alveoli and cells have 

 a different structure from the rest of the gland. In Hydrophiinae the inter- 

 alveolar connective tissue is extensively developed, most noticeably in Enhy- 

 drina hardwickii. Platurus fasciatus is conspicuous for the small size of the 

 external alveoli, especially at the posterior end of the gland. The duct of 

 this group is remarkable for the convoluted course its terminal portion takes. 

 Small lobules are found arranged as in the other Proteroglyphous Colubrina;. 

 In Platurus fasciatus these glands are reduced almost to single alveoli with a 

 lining epithelium like that of the poison gland itself. But in Distira cyano- 

 cincta and Hydrus platurus they are more markedly developed, a few of 

 them in the latter half of the course of the duct becoming mucus-secreting. 

 Towards the termination of the duct the cells of its own lining epithelium 

 also become mucus-secreting. This has been shown to be common in the 

 duct of the parotid and labial glands of the opisthoglyphous Colubrinae, and 

 it forms a pavement layer in the Crotalinae. 



Thus the Ophidia are the only animals in which a considerable admixture 

 of mucus is present in the parotid secretion, this mucus being derived in all 

 cases from some of the cells of the duct and sometimes from special accessory 

 mucous alveoli. The presence of mucous alveoli in the parotid gland and 

 the conspicuous admixture of mucus in the parotid secretion, more especially 

 of elapine Colubrinae, may perhaps present an analogy to the condition in 

 the submaxillary glands of many mammalia. They are all restricted closely 

 to the exit of the duct. 1 



Johannes Muller (1830) was, however, the first to recognize the tubular 

 structure of the poison gland and the spongy nature of the inner wall of 

 the tubules. He states also that the glandular tubules stretch continuously 

 from the exit duct to the surface of the organ. According to him the structure 

 of the poison gland of Naja haje is as follows: The connective-tissue capsule 

 of the gland consists of a single layer, but not of double, serous space embrac- 

 ing covers, as is the case of Vipera, while a wide, rather indefinite lymphatic 

 space is present between the poison gland and the upper wall of the oral 

 cavity beneath. Emery (1875) distinguishes two parts in the poison gland of 

 Naja haje. The posterior part is considered as the poison gland proper, 

 the anterior part as belonging to the mucous system, in which all supralabial 

 glands are to be enumerated. In the posterior part the cells near the central 

 zone are cylindrical, while those lining the peripheral zone are flattened 

 epithelia. In the anterior part there are also cylindrical epithelia, but they 

 are somewhat larger and have a much clearer nucleus not many granular 

 particles around the nucleus which is always easily seen. In fact, these 



1 West. Jour. Linn. Soc., 1898, XXVI, 517. 



