26 ANATOMY OF A CHELONIAN. 



53. The Mandible is a V-shaped mass, composed of 

 several bones, and presents an anterior dorso-ventrally 

 compressed body^ and two lateral rami, one at the poste- 

 rior end of each half of the body, and compressed later- 

 ally. On the upper border, on each side, is a prominent 

 coronoid process where ramus and body meet ; and on the 

 free end of the ramus is an oblique surface, with a cen- 

 tral elevation, which articulates with the ventral end of 

 the quadrate {z^^, which has a corresponding groove 

 into which the ridge fits, so that a firm hinge-joint is 

 formed between them. On the upper surface of the 

 body are ridges, which bear the horny cutting plates 

 of the lower jaw (4, a). On the upper edge of the ra- 

 mus is a fissure leading into the mandible ; a branch of 

 the inferior maxillary nerve (191) enters there. On the 

 inner side of the ramus are two foramina ; through the 

 lower a branch of the above nerve passes out into the 

 floor of the mouth. 



54. The following parts enter into the composition 

 of the mandible ; to separate them needs some patience, 

 as the bones adhere very tightly and the lines of artic- 

 ulation are not very visible. 



a. On the posterior aspect of the bony body of 

 the mandible is a groove, filled in the recent 

 skeleton by a cartilaginous rod {MeckeVs 

 cartilage), which will subsequently be found 

 to extend back through the rami. 



b. Take hold of the articular end of one ramus, 

 and work it to and fro until it is loose. Then 

 carefully detach it, disturbing the remaining 

 bones as little as possible. It will bring with 

 it Meckel's cartilage, which will be found to 



