100 THE VERTEBRATE SKELETON. 



THE LOWER JAW. 



The lower jaw or mandible like that of the Salmon is 

 partly cartilaginous, forming Meckel's cartilage, partly 

 formed of cartilage bone, partly of membrane bone. Meckel's 

 cartilage is of course not seen in the dried skull. 



The lower jaw includes one cartilage bone, the articular 

 (fig. 12, 9), this is a large bone connected by a saddle- 

 shaped surface with the quadrate. Meckel's cartilage lies in 

 a groove on its under surface, and projects beyond it in front. 

 The angular is a small thick bone united to the lower surface 

 of the articular at its posterior end. The dentary (fig. 12, 10) 

 is a large tooth-bearing bone meeting its fellow in the middle 

 line in front, while the articular fits into a deep notch at its 

 posterior end. 



THE HYOID ARCH. 



The hyomandibular (fig. 12, 7) is a large irregular bone, 

 articulating by a prominent rounded head with the spbenotic 

 and pterotic. It is united in front with the meta-pterygoid 

 and symplectic, and sends off behind a strong process which 

 articulates with the opercular. The symplectic is a long 

 somewhat triangular bone drawn out in front into a process 

 which fits into a groove on the inner surface of the quadrate. 

 The distal portion of the hyoid arch is strongly developed and 

 consists of first the inter-hyal (fig. 12, 11), a short bony rod, 

 which articulates dorsally with a patch of cartilage intervening 

 between the posterior part of the hyomandibular and the sym- 

 plectic. Below it is united with the apex of the triangular 

 epi-hyal, a bone suturally connected with the large cerato- 

 hyal (fig. 12, 13) which unites distally with two small hypo- 

 hyals. To the cerato-hyal are attached a series of seven 

 strong curved cylindrical rods, the branchiostegal rays. The 

 first of these is the smallest and they increase in size up to the 

 last. The four dorsal ones are attached to the outer surface 

 of the cerato-hyal, the three ventral ones to its inner surface. 



