i6o ALUS. [Vol. XVIII. 



gives to the edge a scalloped appearance. The edge is thin, 

 and presents slight concentric markings similar to those found 

 on the scales of the body. The ventral edge of the process 

 is thickened, is slightly concave, and lies in a nearly hori- 

 zontal position. The anterior, or basal half of this ventral edge 

 of the process is connected by a strong web of bone with the dorsal 

 part of the mesial wall of the grooved part of the bone, and so 

 forms a continuation of that wall. A similar web of bone is found 

 along the mesial edge of the proximal process of the bone. It is 

 directed mesially, and is continued downward a short distance 

 along the anterior edge of the grooved part of the bone. These 

 two webs of bone, and the two dorsal processes with which they 

 are associated, together form a part of the clavicle which presents 

 internall}' a large concave surface. In the bottom of this con- 

 cavity there is a depressed region bounded by a narrow curved 

 wall, or surface, which lies perpendicular to the rest of the sur- 

 face of the concavity, and nearly concentric with the anterior and 

 dorsal edges of this part of the bone. It lodges, and forms the 

 surface of attachment of, the dorsal part of the primary shoulder 

 girdle. The dorsal end of the narrow wall that marks the limits 

 of this surface extends backward to about one half the length of 

 the large posterior process of the clavicle, varying in length in 

 different specimens. Its ventral end extends downward to the 

 dorsal edge of the large opening, already referred to, in the mesial 

 wall of the grooved part of the bone. The ventral part of the 

 posterior edge of the latter opening is formed by a pointed process 

 of the clavicle which gives attachment, along its lateral surface, to 

 the ventral end of the primary girdle. 



The dorsal part of the clavicle is relatively straight. In its ven- 

 tral third it curves somewhat sharply forward, and its pointed 

 distal end, which is directed forward and mesially, lies close to 

 and is firmly bound by fibrous tissue to the corresponding end of 

 the bone of the opposite side of the head. The lateral and mesial 

 surfaces of the bone here both give origin to parts of the sterno- 

 hyoideus; the groove of the bone lodging certain of the muscles 

 of the pectoral fin and parts of the muscles of the trunk. The 

 extreme ventro-anterior end of the clavicle gives origin to a liga- 

 ment that has its insertion on the hind end of the sternum. The 



