THE DENTITION OF THE PIG. 317 



year, at which time the first deciduous molar, which is not 

 replaced, falls out. Hence the formula of the permanent denti- 

 tion is i. '^, c. g p,m, 1^3 m. l^^ = 40. 



The permanent incisors in the upper jaw have short, broad, 

 vertically-disposed crowns, and lie in a longitudinal series, the 

 external being separated by an interval from the others. The 

 elongated inferior incisors lie side by side, are greatly inclined 

 forward and upward, and are grooved upon their upper or 

 inner faces. The strong, angulated crowns of the canines are 

 bent upward and outward 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 premolars are all brought to a 

 cutting longitudinal 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 ctecum, in 

 which is a spiral fold of the mucous membrane ; and, at the 

 entrance of the oesophagus, 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 

 toward the pylorus, and foreshadow the more developed struct- 

 ure observable in Ruminants. 



The cfficum has not above one-sixth the capacity^ of the 

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

 efficient ilioc^ecal valve. The liver is provided with a gall- 

 bladder. The heart is devoid of a Eustachian valve, and 

 sometimes, but not always, possesses a septal ossification. 



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

 nominata^ whence the right subclavian and the two carotids 

 arise, and a left subclavian. This is an arrangement 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. 



