372 THE ANATOMY OF VERTEBRATED ANIMALS. 



crowns of the canines are bent upwards and outwards in 

 both jaws. They work against one another, in such a 

 manner, that the upper wears on its anterior and external 

 face, the lower on the posterior aspect of its apex. The 

 crowns of the premolai's are all brought to a cutting longi- 

 tudinal edge, while the molars have broad crowns with 

 transverse ridges subdivided into tubercles. Of these ridges 

 there are two in the anterior two molars of each jaw, while 

 the posterior molar is more complex, having at fewest three 

 distinct ridges. The molar teeth all develop roots; but the 

 canines continue to grow for so long a time, in the Boar, 

 that they might be said to be rootless. 



The alimentary canal is ten or twelve times as long as 

 the body. 



The stomach is less simple in structure than it appears 

 to be at first sight. The cardiac end presents a small 

 ccECum, in which is a spiral fold of the mucous membrane ; 

 and, at the entrance of the cesophagus, the epithelial lining 

 is folded so as to form a sort of valve. Folds of the mucous 

 membrane, between which there lies a groove, extend from 

 the cardia towards the pylorus, and foreshadow the more 

 developed structure observable in Ruminants. 



The ccBcum has not above one-sixth the capacity of the 

 stomach, and the ilium projects into it, so as to form a 

 very efficient iliocsecal valve. The liver is provided with a 

 gall-bladder. The heart is devoid of an Eustachian valve, 

 and sometimes, but not always, possesses a septal ossifi- 

 cation. 



There is only one anterior cava. The aorta gives off an 

 innominata, from whence the right subclavian and the two 

 carotids arise, and a left subclavian. This is an arrange- 

 ment midway between that observed in the Horse and that 

 in Man. 



The trachea, before it divides, gives off a third bronchus, 

 which passes to the right lung ; and the lungs are deeply 

 lobed. 



In the brain the cerebral hemispheres rise above the cere- 

 bellum much more than they do in the Horse. 



