THE HUMAN SPECIES 



covering of mucous membrane. In the pig the glands are 

 disposed superficially, side by side; in the ruminants and in 

 the horse they form more or less circular masses, though here, 

 too, there is no saccular disposition. 1 Man possesses tonsils in 

 common with the reptiles, birds and mammals. In man the 

 tonsil is furnished on either side of the middle line with three 

 or four deep longitudinal grooves and numerous nodules with a 

 diameter of sometimes as much as I mm. 



A further peculiarity of 

 the human mouth lies in 

 the histology of its mucous 

 membrane, neither a stra- 

 tum granulosum, nor a 

 stratum lucidum, being 

 present, nor, with the ex- 

 ception of the lips and a 

 portion of the lingual epi- 

 thelium, is any sign of 

 cornification to be found. 

 The fishes possess a 

 rudimentary tongue in the 

 form of a protuberance, 

 invested in mucous mem- 

 brane, above the hyoid 

 bone, but a muscular, pro- 

 trusible tongue proper we 

 find first in the amphibians. 

 In the reptiles and birds it 

 undergoes further muscular development, though the apex is 

 frequently horny, and only in the parrot is an entirely muscular 

 tongue present. 



The tongue of mammals is essentially fleshy, with its 

 (see Fig. 67) muscular structure, its covering of mucous mem- 

 brane and the numerous differentiations of the same. In all 

 mammals we distinguish the epithelium, the mucous membrane 

 with its papillae (see below), the lamina propria of the mucous 

 membrane, the glands, the muscular structure and the support- 

 ing organs (hyoid bones). In addition, many of the cheiroptera, 



1 Ellenbefger, loc. cit., part iii., pp. 101, 109. 



FIG. 66. Mouth, palate and pharynx. 

 (Thome, Zoologie.) a, tongue ; bb', pala- 

 tine arch ; cc', palat. pharyng. arch ; </, 

 velum palat. ; e, uvula ; /, tonsils ; g, 

 porta pharyng. 



