GLANDS OF THE MOUTH 251 



greater morphological complication both as regards number and 

 arrangement takes place. Their histological character also 

 becomes changed in such a manner that the most varied forms 

 of glands may be recognised. 



Amphibians. With the exception of the Perennibranchiata 

 Derotremata, and Gymnophiona, a tubular gland becomes developed 

 in all Amphibia from the anterior portion of the roof of the mouth 

 (com p. Fig. 160), the main mass of which in Urodeles lies in the 

 cavity of the nasal septum or premaxilla (intermaxillary or inter- 

 nasal glancT). In Anura its position is more anterior than in 

 the Urodela, and it is more largely developed ; but in both cases 

 the ducts open on to the anterior part of the palate. 



In Anura there is a second gland (pharyngeal gland) present in 

 the region of the internal nostrils, the secretion of which passes 

 partly into the latter and partly into the pharynx. 



Numerous gland-tubes are also present in the tongue of 

 Amphibians, and in the Gymnophiona oral glands are abundant. 



Me :- Km 



Gc 



FIG. 201. THE POISON- APPARATUS OF THE RATTLESNAKE. 



S, the fibrous poison-sac, which is surrounded by the constrictor-muscle, Me at 

 J/c 1 an extension of the latter towards the lower jaw can be seen ; Gc, the 

 duct arising from the poison-gland, which passes into the poison-fang at f ; 

 the latter is embedded in a large sac of the mucous membrane, zf; Km, 

 masticatory muscles, some of which are seen cut through at * ; posterior to 

 this the cut edge of the scaly integument is seen ; oV, external nostril ; A, 

 eye displaced towards the antero^dorsal aspect ; z, tongue ; za, aperture of the 

 poison-fang. 



Reptiles. The mouth-glands in Reptilia show an advance, on 

 those of Amphibia inasmuch as they are separated into groups. 

 Thus not only is there a palatine gland, homologous with the 

 intermaxillary gland, but lingual and sublingual, as well as upper 

 and lower labial glands are present. Chameleons and Snakes 

 are distinguished by a remarkable richness in glands, which 

 become most specialised into definite groups in the latter. In 

 poisonous Snakes the poison-gland becomes differentiated from 

 a portion of the upper labial gland. It is enclosed in a strong 



