Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. 



119 



oral ends of the curved bases of the processes reach this Hne. As 

 the number of processes on the two sides of each arch is not ex- 

 actly the same, the processes are not all placed in pairs, though 

 many of them are approximately so arranged. The processes on 

 the antero-lateral surface of the first arch are placed much more 

 upon the oral surface of their arch than the other processes are, 

 and their flat surfaces are presented, approximately, dorsally and 

 ventrally. The flat surfaces of the other processes are presented 

 anteriorly and posteriorly, or laterally and mesially, according as 

 they lie on the anterior or posterior surfaces of an arch. The oral 

 edges of all the processes are lined with bristles that seem to be 

 of the same bony composition as the supporting rays of the gill 

 filaments. They are jointed, at their bases, with a rod of similar 

 composition, which extends into the substance of the process (Figs. 

 40 and 43) . The bristle and rod are both hollow, and a blood vessel 

 or capillary space could be traced into them under the microscope. 

 The oral surfaces of the pharyngeal bones are covered with sim- 

 ilar bristles, but their edges are not furnished either with proc- 

 esses or bristles. The bristles on these pharyngeal bones are 

 stronger than those on the processes of the arches, and they are 

 strongly curved and horn-shaped, the hollow of the curve being 

 serrated. By this arrangement of processes and bristles the arches 

 of the fish become a veritable sieve through which all the water 

 that traverses the gill chamber is strained. 



Between the dorso-anterior end of the first branchial arch and 

 the demibranch, there is a narrow space, or line, along which the 

 lining membrane of the gill chamber lies directly upon the lateral 

 surface of the skull. This line lies immediately in front of the 

 internal carotid foramen, and extends from near the ventral edge 

 of the skull upward and slightly backward to the lower edge of the 

 facial foramen. Its ventral end is connected with the correspond- 

 ing end of the line of the opposite side of the head by a transverse 

 groove on the dorsal surface of the mouth cavity, the groove lying 

 immediately in front of the superior pharyngeal bones. The upper 

 end of the line, on each side of the head, lies slightly in front of 

 the plane of the blind, anterior end of the saccular recess of the 

 cranial cavity. Immediately ventral to its upper end the line lies 

 approximately external to the anterior edge of the depression that 



