Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. 129 



is somewhat wider than the posterior two thirds, and is scoop- 

 shaped, the hollow of the scoop directed mesially. The inferior 

 edge of the scoop projects ventrally and mesially as a thin 

 ridge of bone, and the groove on the ventral surface of the element 

 continues forward, antero-lateral to it, that is, along the posterior 

 half of the ventro-lateral, or external surface of the scoop. Be- 

 tween the hind edge of the scoop and the postero-mesial edge of 

 the shank of the bone there is a groove which leads from the main 

 groove on the ventral surface of the element into the hollow of the 

 scoop. It transmits the nerve and artery of the arch. Both ends 

 of the bone are capped with cartilage, the anterior end articulating, 

 as already stated, with the small median piece of cartilage that rep- 

 resents the fused hypobranchials of the fourth pair of arches, and 

 also often wdth the middle portion of the posterior articular cap 

 of the third hypobranchial. The dorsal corner of the anterior cap 

 touches, or nearly touches, in the middle line the corresponding 

 corner of the element of the opposite side of the head. 



The Fifth Ceratobranchial (CB, V) is usually slightly 

 shorter than the anterior ones. It may be said to consist of three 

 parts, a slender, curved, rod-like part, somewhat similar to the 

 anterior ceratobranchials, and two processes, one directed ventrally 

 and the other mesially. The rod-like part of the bone is doubly 

 curved, the hollow of one curve presented antero-laterally, that 

 of the other presented dorsally. Both ends of the rod are capped 

 with cartilage, the end of the anterior cap touching or almost 

 touching, in the middle line of the head, its fellow of the opposite 

 side. Between these anterior ends of the two elements lies the 

 small cartilaginous fourth basibranchial, with which both of the 

 ceratobranchials articulate. The ventral process of the piece arises 

 from the middle three fifths of the ventral surface of the rod. Its 

 antero-lateral surface is slightly concave ; its postero-mesial sur- 

 face slightly convex. Its ventral edge is thin and rounded. The 

 mesial process of the piece is a thick, somewhat triangular plate, 

 the base of the triangle rounded and directed posteriorly. The 

 dorsal surface of the plate is slightly concave, the ventral surface 

 slightly convex. The process arises from the dorsal edge, or 

 dorsal surface of the rod of the piece, the extent of the region 

 of origin corresponding approximately to that of the ventral 



