Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. 141 



smaller than the dorsal one and articulates with the lateral surface 

 of the skull in the facet on the lateral surface of the postorbital 

 ossification. The articular surface on the posterior process gives 

 articulation to the operculum. 



Between the ventral edge of the anterior process of the hyoman- 

 dibular and the anterior edge of the shank of the bone below it, 

 there is a wide, thin plate, apparently of membranous origin. It 

 lies on a level with the internal surface of the hyomandibular and 

 gives to that aspect of the bone a large and nearly flat surface. 

 The lateral aspect of the bone, on the contrary, is an irregular sur- 

 face. It is separated into anterior and posterior portions by a 

 strong ridge of bone which extends from the ventral end of the 

 element upward and forward, in a slightly curved line, almost to 

 its dorsal end. The ridge projects laterally and backward, and its 

 posterior surface forms, with the posterior portion of the lateral 

 surface of the bone, a deep groove, which is practically a groove 

 on the posterior or dorso-posterior edge of the element. The 

 dorsal end of the preoperculum fits into the dorsal part of this 

 groove, the dorsal end of that bone coming to, or extend- 

 ing slightly above, the dorsal end of the ridge on the hyoman- 

 dibular, the two bones being firmly united by fibrous tissues. Ven- 

 tral to its dorsal end the anterior edge of the preoperculum curves 

 downward and forward and lies at first external to the ventral end 

 of the hyomandibular, and then, ventral to that bone, external to 

 the adjoining dorsal end of the symplectic. 



The middle portion of the anterior surface of the ridge on the 

 hyomandibular fits against the dorsal portion of the hind edge of the 

 metopterygoid, the latter bone lying external to that thin plate-like 

 portion of the hyomandibular that fills the angle between the ridge 

 and the anterior process of the bone. A short process on the pos- 

 terior edge of the metapterygoid projects backward, internal to 

 this plate-like portion of the hyomandibular, and also internal to 

 the shank of the bone beyond it. The two bones are thus here 

 firmly held together by bony processes, as well as by the fibrous 

 tissues that connect them, tne hyomandibular becoming, in appear- 

 ance, a part of the palato-quadrate arch. 



Between the hind edge of the hyomandibular and the anterior 

 edge of the preoperculum, where the latter bone turns forward 



