SALIVARY GLANDS IN THE HOKSE. 21 



The upper surface of the tongue is covered all over with 

 numerous projections or eminences termed papillge. They are 

 distinguished into orders according to their size and form. 

 These different kinds of papillse are highly vascular and sensi- 

 tive prolongations of the mucous coat of the tongue. When 

 injected they seem to consist entirely of capillary vessels. 

 Nerve-tubes also seem universally to penetrate into the papillae. 

 The papilke are at once the seat of a high degree of tactile sen- 

 sibility, and are also the parts chiefly concerned in the special 

 sense of taste. 



Salivary Glands. The salivary glands supply the saliva 

 with which the aliment is mingled during mastication. There 

 are three principal glands of this sort on each side, which are 

 respectively named the parotid, the submaxillary, and the sub- 

 lingual. Of these the parotid lodged in the space between 

 the angle of the jaw, the zygomatic arch, and the mastoid pro- 

 cess is the largest ; the submaxillary gland, on the inside of 

 the jaw near its angle, is next in size ; and the sublingual, 

 beneath the tongue, is the smallest of all. 



The parotid saliva of the horse is usually perfectly limpid 

 and colourless, devoid of smell and taste, incapable of being 

 drawn out into threads, and of a distinctly alkaline reaction. 

 Its density very little exceeds that of pure water (1.0051 to 

 1.0074). It contains potash, soda, and lime, combined with an 

 organic matter named ptyalin ; an extractive matter soluble in 

 alcohol and in water, precipitable by tannic acid ; sulphocyanide 

 of potassium ; the potash-salt of an acid belonging to the 

 butyric group ; epithelium and mucous corpuscles ; the 

 chlorides of sodium and potassium ; phosphates ; alkaline 

 sulphates. 



The salivary glands are of large proportionate size in the 

 horse, and the secretion of saliva appears to be great in the 

 same proportion. In no mammal but the ruminants does the 



