Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. ^y 



of the dilatator groove. The mesial edge of this inferior surface 

 of the process connects by suture with a part of the lateral edge 

 of the parietal. 



On the lateral surface of the body of the bone, close to its dorsal 

 edge, there is a long, deep, oval facet, which gives articulation 

 to the posterior of the two articular heads of the hyomandibular. 

 This facet begins, posteriorly, at the base of the posterior process 

 of the squamosal, and runs forward and slightly downward almost 

 to the anterior edge of the body of the bone. The edge of the 

 bone, immediately in front of and below the anterior end of the 

 facet, is overlapped by the splint-like sutural processes of the 

 petrosal, the points of the splints almost reaching to the edge of 

 the facet. The axis of this facet inclines downward considerably 

 less than the facet on the postorbital ossification. 



The body of the squamosal is traversed by the external semi- 

 circular canal, which enters and leaves the bone on its thick inferior 

 edge. This edge of the bone is united by sutare or synchondrosis 

 with the adjoining bones, and no part of it is exposed on the 

 inner surface of the skull. Parts of it can, however, be seen, from 

 the cerebral cavity, at the bottoms of the two openings, one of 

 which leads into the anterior end of the external semicircular canal, 

 and the other into the recess that lodges the sinus utriculi posterior. 



The superior laminar process of the squamosal is traversed by 

 the otic section, and by what Ewart (No. 24) calls the temporal 

 section of the main infraorbital lateral canal, and it represents, as 

 already stated in one of my earlier works (No. 9), that part of the 

 bone that is developed in relation to that canal. The posterior 

 process of the bone gives insertion to a ligamentous fascia that 

 covers externally a part of the anterior surface of the first muscle 

 segment of the trunk. It is developed in connection with that 

 fascia, and represents a fibrous or membranous component of the 

 bone. The body of the bone is of perichondria! or endochondrial 

 origin, whichever it may be, and is undoubtedly developed in some 

 relation to the external semi-circular canal. There are, thus, in 

 the squamosal of Scomber, three separate components ; a so-called 

 primary one represented in the body of the bone, a dermal one 

 represented in that part of the bone that encloses the lateral canal, 

 and a fibrous or membranous one represented in its posterior 

 process. 



