282 . UNGULATA 



but curving strongly outwards, upwards, and finally inwards, while 

 those of the lower jaw are directed upwards and outwards with 

 a gentle backward curve, their hinder edges working and wearing 

 against the front edges of the upper canines. 1 They appear 

 externally to the mouth as tusks, the form of the upper lip being 

 modified to allow of their protrusion, but are much less developed 

 in the females than in the males. The teeth of the molar series 

 gradually increase in size and complexity from first to last, and 

 are arranged in contiguous series, except that the first lower 

 premolar is separated by an interval from the second. First and 

 second upper premolars Avith compressed crowns and two roots. 

 The third and fourth have an inner lobe developed on the crown, 

 and an additional pair of roots. The first and second true molars 

 have quadrate crowns, with four principal obtuse conical cusps, 

 around which numerous accessory cusps are clustered. The length 

 of the third molar is nearly equal (antero-posteriorly) to that of 

 the first and second together, its crown having, in addition to the 

 four principal cusps, a large posterior talon or heel, composed of 

 numerous clustered conical cusps, and supported by several additional 

 roots. The lower molar teeth resemble generally those of the upper 

 jaw, but are narrower. Milk dentition : i f , c ^, m f ; total 28, 

 the first permanent premolar having no predecessor in this series. 

 The third incisor, in both upper and lower jaws, is large, developed 

 before the others, and has much the size, form, and direction of 

 the canine. Vertebne : C 7, D 13-14, L 6, S 4, C 20-24. The hairy 

 covering of the body varies much under different conditions of 

 climate, but when best developed, as in the European Wild Boar, 

 consists of long stiff bristles, mostly abundant on the back and 

 sides, and of a close softer curling under-coat. 



The skull of the Pigs (Figs. 1 03-1 05) has the axis of the face 

 bent down upon the basicranial axis, as is also the case with the 

 Sheep. Its most striking feature is the elevation and backward 

 slope of the occipital crest formed by the union of the supraoccipital 

 and parietals. The broad and flat frontals have small postorbital 

 processes, which do not join the zygomata, so that the orbits are 

 open behind. The nasals are very long and narrow ; and the pre- 

 maxillae send up long nasal processes, stopping short of the frontals. 

 A peculiar prenasal bone is developed at the anterior extremity of 

 the mesethmoid, which serves to strengthen the cartilaginous snout. 

 The palate is long and narrow, and extends behind the last molar 



1 If from any accidental circumstances these teeth are not constantly worn 

 down by friction, they grow into a complete circle, the point penetrating the 

 bone of the jaw close to the root of the tooth. The natives of the Fiji Islands 

 avail themselves of this circumstance to produce one of their most valued orna- 

 ments a circular boar's tusk : the upper canines being extracted, the lower ones 

 are allowed to grow to the desired form. 



