Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. j^I 



hind end of the sternum, in its natural position, lies slightly dorsal 

 to the anterior end of the clavicle. 



Associated with the clavicle there are two accessor}^ bones. The 

 smaller of the two is oblong in shape, with a convex external and 

 a concave internal surface. Its superior edge is thin and rounded, 

 with concentric scale-like markings. Its inferior edge is thick- 

 ened and nearly straight. The bone is bound by fibrous tissue to 

 the inner surface of the postero-dorsal process of the clavicle, 

 and is so placed that its dorso-anterior end fills the scalloped inden- 

 tation in the dorsal edge of that process. The larger accessory 

 bone is somewhat shield-shaped in outline, its postero-ventral end 

 being prolonged in a long and slender spine-like process. At 

 about the dorsal third of its nearly straight antero-dorsal edge 

 there is another process, also long and slender but much less so 

 than the postero-ventral one. It lies along and is bound by fibrous 

 tissue to the inner surface of the anterior accessory bone, near its 

 ventral edge. This larger accessory bone is the oropterygium of 

 certain authors. 



The Primary Shoulder-Girdle contains six ossifications, all 

 of which are surrounded, and united more or less completely with 

 each other, by narrow lines of cartilage. The two largest of these 

 six ossifications are the scapulare and procoracoid of Gegenbaur's 

 descriptions (No. 28). The four smaller ones are the second, 

 third, fourth and fifth basal, or carpal, bones of the same descrip- 

 tions. 



The Scapulare (SC) and Procoracoid (PC), which are sepa- 

 rated from each other by only a narrow line of cartilage, together 

 form a fiat triangular or trapezoidal piece. The ventro-posterior 

 edge of this piece is formed entirely by the procoracoid, and is free 

 and not lined with cartilage. The anterior edge is formed by 

 both the scapulare and the procoracoid, and is attached, through- 

 out its entire length, to the clavicle, excepting only in that part 

 that lies opposite the large opening cut out of the hind edge of 

 the mesial plate of the grooved part of the latter bone. Opposite 

 that opening the opposing edge of the procoracoid is also deeply 

 cut out, a large oval fenestra thus being formed, which, in the 

 natural state, is closed by membrane. Dorsal to this fenestra the 

 articulating edge of the procoracoid, and dorsal to that bone the 

 corresponding edge of the scapulare, are lined with cartilage. 



