GLANDS OF THE MOUTH. 



221 



the glands are mostly arranged in groups; in the higher types, on 

 the contrary, the last- mentioned form, which is considerably higher 

 from a developmental point of view, is the more usual. 



Amphibia. With the exception of the Perennibranchiata, 

 Derotremata, and Gymiiophiona, a tubular gland becomes 

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

 the mouth (comp. Fig. 144, ID], the main mass of which lies, in 

 Urodeles, in the cavity of the nasal septum or premaxilla 

 (intermaxillary or internasal gland). 



In Anura its position is more anterior than in Urodeles, 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 

 Amphibia. 



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 in- 

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

 and lower labial glands are present. Chameleons and Snakes 



FIG. 182. THE POISON-APPARATUS OF THE RATTLESNAKE. 



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



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 t ; 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 ; N, external nostril ; A, eye displaced towards the 

 antero-dorsal aspect ; s, tongue ; za, aperture of the poison-fang. 



are distinguished by a remarkable richness in glands, which become 

 most specialised into definite groups in the latter. In poisonous 

 Snakes the poison-gland (glandula venenata) becomes 

 differentiated from a portion of the labial gland in the upper 

 lip. It is enclosed in a strong fibrous sheath, and is acted upon 



