144 THE VERTEBRATE SKELETON. 



a ventral view is seen to meet the maxillae and vomero- 

 palatines, and in a dorsal view to send back a nasal process 

 (fig. 21, A, 1) between the nasals. 



The maxillae are large bones, each terminating in a point 

 posteriorly. A single row of teeth similar to those on the 

 vomero-palatines runs along the outer margin of the maxillae 

 and prem axillae. 



The posterior part of the upper jaw forms a mass of 

 cartilage which extends forwards towards the maxilla as a 

 long pointed process whose ventral surface and sides are over- 

 lapped by a membrane bone, the pterygoid (fig. 21, 12). 



The suspensorial bones include the quadrate and squa- 

 mosal. The quadrate (fig. 21, 15) which forms the true 

 suspensorium is directed forwards and outwards, and is 

 terminated by a patch of cartilage with which the mandible 

 articulates. 



The lower jaw or mandible remains partly cartilaginous, 

 while its ossifications include two membrane bones and one 

 cartilage bone. The cartilage bone is the articular (fig. 21, C, 

 18), it forms the posterior part of the ramus, extends forwards 

 for some distance along its inner side, and is terminated 

 posteriorly by a patch of cartilage which articulates with the 

 quadrate. The dentary (fig. 21, C, 20) is a large bone which forms 

 the anterior part and nearly all the outer half of each ramus, 

 and bears teeth similar to those of the upper jaw. Attached 

 to its inner face is a long slender splenial (fig. 21, C, 21). 



THE HYOID APPARATUS. 



This consists of the hyoid arch and part of the first two 

 branchial arches. 



The hyoid arch (fig. 21, A, 2) consists of a pair of cornua, 

 each of which is divided into two halves. The dorsal half 

 forming the cerato-hyal is mainly ossified though tipped with 

 cartilage, and is connected by ligament with the suspensorium. 

 The ventral half (hypo-hyal) is cartilaginous, and is connected 

 with the basi-branchial. 



