54 ■ FISHES. 



extremity. Both the maxillary and intermaxillary lie and 

 move parallel to each other, being connected by a narrow 

 membrane ; in many other fishes their relative position is very 

 different. 



The mandible or lower jaw consists of a right and left 

 ramus ; their union by a ligament in front is called symphysis. 

 Each ramus is formed of several pieces ; that which, by a 

 sigmoid concavity articulates with the quadrate, is the 

 articulary bone (35) ; it sends upwards a coronoid process, to 

 which a ligament from the maxillary and the masticatory 

 muscles are attached ; and forwards a long-pointed process, 

 to be sheathed in the deep notch of the anterior piece. A 

 small separate piece (36) at the lower posterior angle of the 

 mandible is termed angular. The largest piece (34) is tooth- 

 bearing, and hence termed dentary ; at its inner surface it is 

 always deeply excavated, to receive a cylindrical cartilage, 

 called Meckel's cartilage, the remains of an embryonic con- 

 dition of the jaw, the articulary and angular being but ossified 

 parts of it. In other Teleostei this number is still more in- 

 creased by a S2)lenial and other bones. 



The infraorbital ring of bones (Fig. 23, 1^) consists of 

 several (four) pieces, of which the anterior is the largest, and 

 distinguished as praorbital. 



The QO-C2i\\.Qdi2)rmoperculum (30) belongs rather to the bones 

 of the suspensorium of the mandible, presently to be described, 

 than to the opercles proper. It is narrow, strong, angularly 

 bent, so as to consist of a vertical and horizontal limb, with 

 an incompletely closed canal running along both limbs. As 

 it is quite a superficial bone, and frequently armed with 

 various spines, its form and configuration form an important 

 item in the descriptive details of many fishes. 



The principal piece of the gill-cover is the operculum (28), 

 triangular in shape, situated behind, and movably united 

 with, the vertical limb of the praoperculum. There is an 



