1^8 ALUS. [Vol. XVIII. 



the groove extending forward into the anterior end of the bone 

 and there forming a triangular recess, which lodges the anterior 

 end of Meckel's cartilage. The anterior end of the bone turns 

 slightly mesially, and articulates with its fello.w of the opposite 

 side by a 'straight and roughened edge which is not capped with 

 cartilage. On the mesial surface of the anterior end of the bone 

 there is a longitudinal depression which marks the line of insertion 

 of the intermandibularis. 



The ventral arm of the dentary is traversed by the anterior part 

 of the mandibular lateral canal. 



Meckel''s Cartilage (M) is a cylindrical rod of cartilage which 

 extends directly forward from the blunt process at the angle be- 

 tween the dorsal and ventral processes of the head of the articular 

 into the angular space between the two arms of the V-shaped 

 dentary. Its anterior end penetrates the dentary, and can be 

 traced a considerable distance toward the anterior end of the bone. 

 Beyond its anterior end the line of the cartilage is continued for- 

 ward toward the tip of the mandible by a special portion of the 

 bone, which can often be separated in dissection as a separate and 

 somewhat spongy or porous rod. The cartilage lies, in its free por- 

 tion, against the mesial surface of the longitudinal portion of the 

 articular, and upon the dorsal surface of the ventral arm of the 

 dentary. 



4. Shoulder Girdle, Stcrnnni and Pectoral Fin. 



The Sternum (S, Fig. 49) is a long flat bone lying in the me- 

 dian plane of the body, between the two sternohyoid muscles. Its 

 dorsal edge is nearly straight, its ventral edge convex. At its hind 

 end it gives insertion to ligaments that connect it loosely with 

 the ventro-anterior ends of the clavicles. At its anterior end it 

 gives origin to two ligaments, each of which has its insertion on 

 the hypohyal of its own side of the head, on an eminence, already 

 described, near the ventral edge of the anterior end of the element. 

 The dorsal edge of the bone is thin ; the ventral edge is consider- 

 ably thickened, lies immediately internal to the integuments of the 

 ventral surface of the head, and has a median V-shaped groove ex- 

 tending longitudinally its full length. 



