430 



ZOOLOGY 



SECT. 



7n.azc.trb/- 



are here entirely absent, and there is a considerable space, or dias- 

 tema, as it is termed, between the incisors and the teeth next in 

 order the pre-molars. Of these there are three in the upper jaw 

 and two in the lower. They are long, curved teeth devoid of fangs, 

 the first smaller than the others and of simple shape, the rest grooved 

 longitudinally on the outer side and with two transverse grooves. 

 bounded by ridges, on their crowns. The first pre-molar of the 

 lower jaw has .two grooves and three ridges ; the second is similar 

 to those of the upper jaw. Behind the pre-molars are the molars, 

 three on each side both in the upper and lower jaws. These 

 are similar to the upper pre-molars, except the last, which is small 

 and of simple shape. 



Opening into the cavity of the mouth are the ducts of four 

 pairs of salivary glands the parotid, the infraorbital , the sub- 

 maxillary (Fig. 1025, s. mx. gl.), and the sublingual (s. gl.}. On 

 the floor of the mouth is the muscular tongue, covered with a 

 mucous membrane which is beset with many papillae. The roof 



of the mouth is formed 

 by the palate. The 

 anterior part, or hard 

 palate, is crossed by a 

 series of transverse 

 ridges of its mucous 

 membrane. The pos- 

 terior part, or soft 

 palate, ends behind in 

 a free pendulous flap 

 in front of the opening 

 of the posterior nares. 

 At the anterior end of 

 the palate is a pair 

 of openings the nasc- 

 palatine canals or an- 

 terior palatine canals, 

 leading into a pair of 

 tubular structures - 

 the organs of Jacobson 

 (Fig. 1024, jcb.} en- 

 closed in cartilage and 

 situated on the floor 

 of the nasal cavities. 

 Behind the mouth or 

 buccal cavity proper 

 is the pharynx. The 

 pharynx is divided 



into two parts, an upper or nasal division, and a lower or buccal 

 division, by the soft palate. Into the nasal division open in front 

 the two posterior nares, and at the sides the openings of the 



mace 



Icxclcl 



J cb 



. 1024. Lepus cuniculus. Vertical section through 

 the anterior part of the nasal region of the head. iiic. 

 section of larger incisor tooth ; jcb. lumen of Jacobson's 

 organ, surrounded by cartilage ; Icr. <lct. lacrymal duct ; 

 nut.?, maxilla ; mas.trb. maxillary turbinals ; nnx. nasal 

 bone ; mis. pal. naso-palatine canal ; sept. cart, cartilagin- 

 ous nasal septum. (After Krause.) 



