Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. 127 



The middle portion usually articulates with the lateral corner of 

 the anterior articular cap of the ceratobranchial of the fourth arch, 

 and is often reduced to a small surface which simply forms the 

 outer, rounded end of a strong angle that separates the other two 

 articular regions. This latter form is the one shown in the 

 figures, the fourth ceratobranchials being pulled backward con- 

 siderably out of their natural position, and out of all contact with 

 the third hypobranchials. In some specimens the articulation with 

 the fourth ceratobranchial seemed not to exist at all. The antero- 

 mesial end of the surface that articulates with the small median 

 cartilage, forms the extreme dorso-mesial corner of the element, 

 which thus lies in front of the median cartilage. 



The one or two laminar processes of the piece arise from its in- 

 ternal surface. The larger of these two processes, where there 

 are two, or the single process, where there is but one, arises in a 

 line which extends backward, from the lateral edge of the anterior 

 half of the piece, along its internal surface. Its ventral edge is a 

 direct continuation of the lateral edge of the anterior part of the 

 element, the continuous edge so formed projecting ventro-mesially 

 and lying nearly parallel to the basal line. Its hind end projects 

 backward, beyond its base of origin from the internal surface of 

 the element, and ends in a point approximately opposite the hind 

 end of the entire element. The second process, when found, lies 

 about midway between the first process and the dorso-mesial edge 

 of the element. In some specimens it is a pronounced laminar 

 process, in others simply a slight ridge. It begins at the hind edge 

 of the bone, opposite that angle of the cartilaginous cap of the 

 piece that separates the lateral articular region from the middle 

 one, and runs forward, parallel to the first process, to a point 

 slightly anterior to the hind edge of the base of that process. Its 

 ventro-mesial surface represents the anterior continuation of the 

 grooved ventral surface of the ceratobranchial of the arch. 



The small, anterior end of the element turns slightly outward 

 and is capped with cartilage. The element does not articulate 

 directly, at any place, with the basal line. 



The third hypobranchials of opposite sides of the head enclose 

 between them the posterior portion of the third basibranchial and 

 the posterior half of the truncus arteriosus ; the artery and basi- 



