ORAL GLANDS. 21 



papillae, or in the larvae of the anura, where, besides the horny 

 jaws, there are numbers of minute cornified teeth. Mention 

 may also be made here of the oesophageal teeth of the snake 

 Rhachiodo7t, which consist of ventral processes of the cervical 

 vertebrae, each with its cap of enamel. These project through 

 the dorsal wall of the oesophagus, and serve to cut open the 

 eggs upon which these reptiles feed. 



Tongue. — The tongue is primitively a fleshy fold of the floor 

 of the mouth, supported to a greater or less extent by some of 

 the elements of the first visceral (hyoid) arch (see skeleton). 

 In the fishes this tongue is without its own muscles, and can 

 be moved only imconnection with the branchial arches. In the 

 cyclostomes, on the other hand, lingual muscles — protractors and 

 retractors — of considerable size appear, while in the amphibia 

 and higher groups similar muscles are usually well developed. ^ 

 In the amphibia the tongue is fastened by its ventral surface or 

 its anterior end. In the reptiles, on the other hand, it is fastened 

 behind. In this group, as in the birds, it is usually horny, with 

 few intrinsic muscles, and in these the hyoid becomes more 

 modified as a lingual skeleton. In the mammals the tongue 

 reaches its highest development, with very considerable varia- 

 tions of form. Beneath the tongue, in many mammals, is a 

 small fold, the sublingua, which is regarded by Gegenbaur as 

 homologous with the tongue of the lower forms, the mammalian 

 tongue being a structure peculiar to that group. 



Oral Glands. — Glands connected with the oral cavity first 

 appear in the amphibia, where in the epithelium occur numerous 

 mucous glands, the secretion of which moistens the lining of 

 the mouth. Besides these, the higher amphibia have a larger 

 internasal gland opening in the palate region. In the reptiles 

 glands are more numerous, occurring on and beneath the tongue, 

 and along the margins of the jaws. From these latter are 

 developed the poison glands of snakes ; while if the lizard Helo- 

 derma be poisonous, its poison is secreted from the large sub- 

 lingual gland. In the birds the glands are not so numerous, 

 those of the tongue, palatal region, and angle of the mouth, 

 being most conspicuous. In the mammals three pairs of glands 



1 Occasionally (Pifa, Dactykthrd) a tongue Is not formed. 



