92 



COMPARATIVE ANATOMY 



Teleostei (Fig. 70), and in this respect such forms as Argyropelecus 

 and Cyclothone acclinidens deserve special mention. The cranial 

 cavity may reach between the eyes as far as the ethmoidal 

 region, or may become reduced to a narrow cartilaginous and 

 fibrous interorbital septum. 



In addition to the general account of the various investing and 

 replacing bones of the skull on pp. 82-84, the following points may 



Sphot pat' soec 



dent 



FIG. 69. CRANIAL SKELETON OF THE SALMON. From the left side. 



art, articular ; branchiost, branchiostegal rays ; dent, dentary ; epiot, epiotic ; tth, 

 supraethmoid ; fr, frontal; hyom, hyomandibular ; into}), interoperculum ; 

 '".'/, jugal ; mpt, mesopterygoid ; mt/>t, metapterygoid ; mx, maxilla ; nas, 

 nasal ; orbital ring ; op, operculum ; jjal, palatine ; par, parietal ; 

 P.iiix, premaxilla ; jtra'p, preoperculum ; pt, Y J terygoid ; pier, pterotic 

 (squamosal) ; Quail, quadrate ; socc, snpraoccipital ; sphot, sphenotic ; sultoj), 

 suboperculum ; Zitnge, tongue. 



be mentioned, and the reader is referred to Figs. 69 and 70 for 

 further details. 



As in Ganoids, the chief roofing bones of the skull are the 

 parietals and frontals, the former of which may be separated from 

 one another by a process of the supraoccipital. Laterally to the 

 frontal is a sphenotic, which extends backwards to the pterotic 

 (squamosal, cf. p. 83). Supratemporals and jugular plates are 

 never present. 



Forming the lateral walls of the skull in the orbital region is 



