— 110 — 



In Hydrocyon also, both articulations are wanting, according to Sagemehl ('84 b, p. 95), and in the 

 Cyprinidae, according to the same author ('91, p. 582), the posterior articulation is replaced by an 

 articulation of the entopterygoid with the ectethmoid. 



OPERCULAR BONES. 



The opercular is so firmly bound by articular ligaments to the stout opercular articular head 

 of the hyomandibular that it is capable of but little movement. From its articular head a stout raised 

 portion runs posteriorly or postero-ventrally across the outer surface of the bone and terminates 

 in the stout opercular spine; the point of that spine extending slightly beyond the point of the large 

 preopercular spine and lying slightly dorsal to it. 



The subopercular is an angular bone that embraces the ventral corner of the opercular. It 

 bears a short, small spine at its ventral corner. 



The interopercular is long and tapering. Its broad hind end is bound by tissue to the ventral 

 portion of the anterior edge of the subopercular, but it is separated from that edge by a considerable 

 interval, bridged by a connecting sheet of tissue. Its pointed anterior end is bound by ligament to 

 the lateral surface of the hind end of the mandible. 



M A N D I B L E. 



The mandible is long and rather slender, and has angular, articular and dentary elements 

 that ofEer no special peculiarities. The dentary lodges three latero-sensory organs, and the articular 

 one organ. The summit of the coronoid process of the articular is separated by a considerable interval 

 from the hind end of the dorsal limb of the dentary, the intervening space being filled by a tough 

 päd of fibrous tissue. In the mandibular labial fold there is a gristly core, as in Scorpaena, but it is 

 smaller thanlin that fish. ' 



4. MUSCLES. 



The adductor mandibulae of Cottus resembles closely that of Scorpaena. The superficial 

 division, A^, of the muscle arises from the anterior portion of the external surface of the 

 preopercular and runs almost directly forward, lying external to the levator arcus palatini and to 

 the deeper division, AgAg, of the adductor. It terminates anteriorly in a tendinous band which ex- 

 tends the füll length of its anterior edge and is inserted dorsally on the maxillary, while ventrally 

 it joins and becomes part of the tendon A2A3. The deeper division of the muscle, A2A3, is incom- 

 pletely separated into superficial and deeper portions, the superficial portion, A,, lying superficial 

 and ventral to the levator arcus palatini and the deeper portion lying internal to that muscle. The 

 two muscles have their origins, as in Scorpaena, from the anterior portion of the external surface 

 of the preopercular, ventral to the muscle Aj, and from the external surface of the palato-quadrate 

 apparatus. Running almost directly forward, certain fibers of the muscle pass directly into the 

 mandible and are continuous with the fibers of A„, others are inserted on the ventral end of the 

 tendinous band that edges the anterior end of the muscle Aj, while the larger portion have their 

 "Insertion on a tendinous structure that forms on the inner surface of the muscle and runs forward 

 and downward into the mandible. In the mandible this tendon separates into four portions, two 

 of which give origin to the fibers of A„, the other two lying one external to the other and having 

 their insertions on the internal surface of the articular near the hind end of Meckel's cartilage. From 



