TONGUE 329 



main part arises anteriorly to the primitive larval tongue from an 

 originally independent region lying between the lower jaw and 

 basihyoid, and known in the Amniota as the tnberculum impar. 

 To this, however, are added portions belonging to the region of the 

 median part of the hyoid and part of the first branchial arch, as 

 well as extensive lateral ridges belonging to the mandibular 

 region, and this fact accounts for the presence of an additional 

 lingual nerve a branch of the third division of the trigeminal 

 which is wanting in Amphibians. The tongue is provided with 

 numerous sensory organs, but no glands are present within it. 

 It is usually very mobile (least so in Chelonians and Crocodiles), 

 and part of it may be enclosed by a " sheath ' : (Fig. 241). 

 In form and relative size it is much more variable than in 

 Amphibians, and this is especially the case in Lizards, in which 

 the tongue is used for classificatory purposes ( Vermilinguia, 

 Crassilinguia, Brevilinguia, Fissilinguia} : in the Fissilinguia 

 and in Snakes it is forked at the apex. In the Chameleon it is 

 protrusible, as in Spelerpes amongst Amphibians, but the 

 mechanism is different in the two cases. 



Birds. Although the early development of the base of the 

 tongue-rudiment in connection with the hyoid and first branchial 

 arch is apparently similar in all Birds and resembles that seen in 

 Reptiles, many differences are noticeable in its subsequent develop- 

 ment in the various groups of Birds (e.g. Lamellirostres and 

 Fringillidas), and these concern the tuberculum impar and the 

 modification of its anterior region in connection with various 

 functional adaptations. Important differences are seen in the 

 muscles and nerves as compared with Reptiles. A sensory branch 

 of the trigeminal nerve is wanting, and is replaced functionally by 

 the strongly developed glossopharyngeal. 



The tongue of Birds is in general poorly provided with muscles. 

 It usually possesses a horny covering and is provided with papillae 

 and pointed, recurved processes ; it may, as in many Reptiles, be 

 split up at its distal end, being either bifurcated (Trochilida?,) or 

 having a brush-like form. In Woodpeckers (cf. p. 123) the tongue 

 may be thrown far out from the mouth by means of a complicated 

 system of muscles, and it thus serves as a prehensile organ. The 

 tongue is relatively largest in predatory Birds (Rapaces) and 

 Parrots : in the latter it is soft and cushion-like, its size being due 

 not so much to the special development of muscles as to the 

 presence of fat, vessels, and glands. 



Mammals. The tongue reaches its most complete morpho- 

 logical and physiological development in Mammals, and undergoes 

 the most various modifications in form and function. It is as 

 a rule flat, band-like, and rounded anteriorly, is rich in glands 1 and 



1 A gland on the apex of the tongue (gland of Blandin or Nuhn) occurs in 

 Man. the Orang-outan, and Sheep. 



