THE RABBIT. 81 



In the ventral view of the skull (fig. 45) it will be seen 

 that the maxilla sends inwards, to meet its fellow medianly, 

 a plate forming the front part of the hard palate. Behind, 

 the hard palate is completed by the pair of palatine bones, 

 which conceal much of the pre- and orbito-sphenoids, and 

 which run back as ridges on either side of the pre- and 

 basi-sphenoids, hiding the junction of these with the orbito- 

 and ali-sphenoids. These ridges terminate in two small 

 angular bones, the pterygoids, which we shall find represent 

 much more important structures in the lower vertebrata. 



The premaxillse and maxillse bound the sides of the 

 nasal passage, and it is completed above by a pair of 

 membrane-bones, the nasals. Along the floor of the nasal 

 passage, in the middle line, lies a median membrane-bone, 

 the vomer. This embraces in a V-l&e groove the meseth^ 

 moid (nasal septum) above, and lies on the palate. The 

 nasal passages are partially blocked by scroll-like bony 

 ingrowths from the inner aspect of their walls, which in 

 life are covered with mucous membrane, and increase the 

 surface sensitive to smell. The ethmoid sends in the 

 ethmo-turbinal ; the nasal, the naso-turbinal ; and the 

 maxilla, the maxillo-tv/rbinal. In the anterior corner of 

 the orbit there is a small membrane-bone, the lachrymal. 



18. The Lower Jaw (mandible) consists of right and left 

 halves or rami, each of which is a single bone (fig. 46). On each 

 ramus there are three incisors which bite against the three 

 of the upper jaw. Then come a canine, four preinolars, and 

 three molars^ the first of which is blade-like (sectorial tooth), 

 and bites against the similar sectorial tooth (last premolar) of 

 the upper jaw. The third molar is small. The arrangement 

 of teeth is indicated in the following dental formula : 



i. 2J, c. LI, P.M. , M. 



, . 

 or more briefly, 



3.3 1.1 4.4 3.3. 



3.1.4.2. 



3.1.4.3. 



In the case of the rabbit (chap, ii., 4) the dental formula 

 be 2.0.3.3. 



1.0.2.3. 

 ZOOL. 6 



