THE TEETH. 



405 



incisors of the upper jaw are much larger, and persist as 

 functional teeth for about three weeks after birth, lying wedged 

 in between the large and small permanent incisors. For the 

 first three weeks after birth there are therefore three upper 

 incisors on each side in the rabbit ; the first and third being the 

 permanent incisors, and the middle one being the deciduous 

 second incisor, which has not yet been shed. The deciduous 

 molars (Fig. 156, tf, tg) are of considerable size, and persist 



Z.S. F.A. O.F. F 



r iG. 162. — The skull of the Rabbit, from the right side. The middle portion 

 of the zygomatic arch and the right half of the mandible have been 

 removed. (From Marshall and Hurst.) 



A, external pterygoid process of all-sphenoid. AS, ali-sphenoid. B, internal orbital 

 foramen. BO, basi-oocipital. BS, basi-sphenoid. C, occipital condyle. D, mandibular 

 symphysis. EO, ex-occipital. P, frontal. PA, foramen lacerum anterius. FM, 

 foramen lacerum medium. G, orbital groove, for ophthalmia division of trigeminal 

 nerve. I, anterior upper incisor. IP, infra-orbital foramen. IP, inter-parietal. J,lower 

 incisor. L, lacrymal hone. LP, laerymal foramen. M, maxilla. MW, mandible. 

 N, nasal hone. OP, optic foramen. OS, orbito-sphenoid. _P, parietal. PE, par- 

 occipital process of ex-occipital. PL, palatine bone. PM. pre-maxilla. PO, periotic. 

 PT. pterygoid. S, squamosal. SP. stylo-mastoid foramen. SO, supra-occipitaL T, 

 tympanic bone. ZM. zygomatic process of maxilla, cut short. ZS, zygomatic process 

 of squamosal, cut short. ' 



until three or four weeks after birth, when they are pushed out 

 by the permanent premolars developed beneath them. 



A full} 7 formed tooth consists chiefly of dentine, covered on 

 its crown, or grinding surface, with a cap of a very hard and 

 densely calcified substance, the enamel ; and invested, especially 

 round its deeper part or root, by a layer of bony substance, the 

 cement. The dentine is hollowed out by the pulp cavity, in 

 which are lodged the blood-vessels and nerves of the tooth. 



