FISH IN GENERAL. 59 



The lower jaw is composed of two branches, uniting in 

 front, and articulating behind by a hollow facet to the 

 pulley which terminates the jugal (No. 2(3) at that end. 

 These branches are in general only divisible into two bones, 

 the denial (No. 34), supporting teeth upon its upper edge, 

 and the articular (No. 35), where the articulating surface is 

 found. They unite by means of a point of the second enter- 

 ing a socket of the first. There is often a third bone, the 

 angular (No. 36), forming the posterior angle of the jaw, and 

 sometimes a fourth, on the internal face of the articular, and 

 corresponding with the opercular (No. 37) of reptiles. 

 Thus the head of fish contains about sixty bones, and some- 

 times, in consequence of the subdivisions of the superior 

 maxillary, several more. 



The hyo'id bone, and branchiostegous rays, adhering to it 

 by the membrane named also branchiostegous, complete the 

 closing of the large aperture on each side of the head, to the 

 shoulder : the hyoid placed as in the other classes of verte- 

 brata, but attached to the temporal, is composed of two 

 branches, each of five pieces ; the styloid (No. 29), by which 

 the apparatus is suspended to the temporal, two lateral pieces 

 (No. 37 and 38) placed in succession, and forming the main 

 part of the branch (No. 38), attaching itself to the interopercu- 

 lum, and two small bones (No. 39 and 40) placed above each 

 other at the anterior extremity of the branch, serving to join 

 it with the corresponding piece. Before this junction is the 

 lingual (No. 41), as in birds and reptiles, and beneath it, 

 uniting the two branches, is a single bone, which by joining 

 the symphyses of the numerals forms the isthmus (No. 42) 

 which separates the two gills below. Thus the hyoid bones 

 are twelve in number. The rays (No. 43) supporting the 

 branchiostegous membrane, adhere by moveable articulations, 

 and often by mere ligaments, to the inferior edge of the chief 

 pieces of each branch. They vary in number exceedingly, 



