Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. 121 



onto the dorsal surface of the anterior end of the second basibran- 

 chial, and entirely covers the dorsal surface of the line of cartilage 

 that separates the two elements. The basibranchial is much com- 

 pressed laterally, especially in its middle portion, and is every- 

 where about twice as deep as it is wide. Its hind end is nearly 

 twice as wide and twice as deep as its anterior end. Its anterior 

 end lies between the anterior ends of the hypohyals, ventral to the 

 mesial processes on the dorsal edges of those bones, and gives 

 articulation to them. It is overlapped dorsally by the hind end 

 of the basihyal. The articular facet, on each side, that gives articu- 

 lation to the distal end of the first branchial arch lies wholly pos- 

 terior to the bony part of this element. The element is thus, func- 

 tionally, a basihyal rather than a basibranchial. In two of the 

 several specimens examined it was formed of two pieces, the bone 

 being separated into two parts by an irregular, transverse, sutural- 

 like line at about the middle of its length. In one of the two speci- 

 mens in which this separating line was found it seemed artificial, 

 and was so considered ; in the other specimen, .which was the one 

 used for the drawings, the line was certainly natural, though it 

 may, of course, have been due to some accident to the fish. 



The Second Basibranchial (BB^) has the same length as 

 the first, and is connected with the two adjoining elements by 

 synchondrosis, the separating interspaces of cartilage both being 

 thicker at their ventral than at their dorsal edges. Like the first 

 basibranchial it is deeper at its two ends than in its middle portion. 

 Each end is about twice as deep as it is wide. The dorsal edge of 

 the element is smooth and rounded ; its ventral edge is narrow, 

 rough and irregular. The anterior end of its dorsal edge is over- 

 lapped externally by the splint process of the first basibranchial ; 

 and at its posterior end a similar process, arising from it, over- 

 laps slightly the anterior edge of the third basibranchial. On its 

 lateral surface there is a deep, triangular depression, which starts 

 from each end of its ventral edge and reaches almost to the 

 dorsal surface of the bone. This depression is not sufficiently 

 indicated in the drawings. Its anterior edge and portion 

 is occupied by a long articular facet which receives the articu- 

 lar edge of the hypobranchial of the first arch, the facet being 

 directed from above downward and forward at an angle of 



