MAMMALS. 577 



lower jaw narrower than the upper; by all these peculiarities the 

 lateral motion of the lower jaw is facilitated. To these different 

 modifications of the articulation the arrangement also of the muscles 

 corresponds. Thus, for instance, the carnivorous animals have a 

 very powerful temporal muscle, which in most of the rodents is 

 feebly developed; in the ruminants the external pterygo'id muscle 

 is of peculiar strength l . 



With the exception of the true or carnivorous cetacea, all mam- 

 mals have salivary glands ; they are more highly developed in pro- 

 portion as the food is masticated for a longer period, more in the 

 vegetable feeders than in the carnivorous animals. In man three 

 salivary glands are present on each side. The parotid gland lies 

 behind the ascending branch of the lower jaw ; its excretory duct 

 (ductus stenonianus) runs across the masseter muscle, perforates the 

 buccinator muscle, and opens into the cavity of the mouth in the 

 neighbourhood of the molars of the upper jaw. This gland is large 

 in the horse, in the ruminants, in the pachyderms, in the beaver 

 and the kangaroos ; small, on the contrary, in the dog, and particu- 

 larly small (rudimentary) in the seal (Phoca). The submaxillary 

 gland lies on the inside of the angle of the lower jaw, near the 

 frenum of the tongue. In most carnivores and in the edentates it 

 superposes the parotid in size ; in Dasypus, where it extends to the 

 great pectoral muscle, its efferent ducts meet in a muscular oval 

 vesicle which terminates forward in the excretory duct 2 . Lastly, 

 under the anterior part of the tongue, lies the sublingual gland, which 

 is always provided with several excretory ducts (ductus Riviniani), 

 and which in some mammals is wanting. The saliva has not in all 

 mammals the same composition ; in the mean the fluid consists in 

 great part of water, and contains only a very small proportion ( T foy or 

 at least less than -^) of solid matter; namely, salts, mucus, osmazom, 

 and a peculiar matter (saUvin), soluble in water, insoluble in alcohol. 



Besides the proper salivary glands there are many small glands 

 on the inside of the mouth and on the palate (mucous crypts), by 

 the secretions of which the food is moistened. 



1 Compare CDVIER Lemons d'Anat. comp. in. pp. 29 60; TIEDEMANN Zoologie, i. 

 s. 251, 252. 



2 RAPP Anat. Unters. uber die Edentaten (le Aufl.) Tubingen, 1843, 4to, s. 54, 

 PI. vn. A similar extraordinary development of this gland exists in the Ant-eater. 

 See OWEN Trans. Zool. Society, iv. 



VOL. II. 37 



