202 



ZOOLOGY 



SECT. 



S.0r 



T.C> 



Pa.ch, 



JIM 



G.ffy JU[y M<1( Sy 

 FIG. 872.^-Skull of young Salmon, second week after hatch- 

 ing ; the investing bones removed. Au. auditory capsule ; 

 Br. 1, first branchial arch ; Ch. notochord ; C. Hy. hyoid 

 cornu ; Fo. fontanelle ; G. Hy. basihyal ; H. Hi/, hypohyal ; 

 H. M. hyomandibular ; 7. Hy. interhyal ; I 1 , V-, labial carti- 

 lages ; Mck. Meckel's cartilage ; M. Pt. metapterygoid 

 region of primary tipper jaw ; Pa. ch. parachordal ; PI. Pt. 

 palatopterygoid region ; Qu. quadrate region ; S. Or. supra- 

 orbital region of cranium ; Si/, symplectic region of sus- 

 pensorium ; T. Cr. cranial roof ; Tr. trabecula ; //, optic 

 foramen ; V, trigeminal foramen. (From Parker and 

 Bettany's Morphology of the Skull.) 



in the median plane, between the muscles of the right and left 



sides, and more 

 numerous than the 

 myomeres of the 

 regions in which 

 they occur. Their 

 distal ends are 

 broadened, and with 

 them are connected 

 the second series 

 (PTG. 2) in the 

 form of small dice- 

 box-shaped bones ; 

 to these, finally, are 

 attached small 

 nodules of cartilage 

 (ptg. 3) forming the 

 third series of 

 radials. The dermal 

 fin-rays or lepi- 

 dotrichia (D.F.R.), 

 which lie in the 



substance of the fin itself, are slender bones, jointed like the antennae 



of an Arthropod, and mostly branched in the sagittal plane (Fig. 876, 



D.F.R.). Each is formed of distinct right 



and left pieces (Fig. 873), in close contact for 



the most part, but diverging below to form 



a forked and dilated end, which fits over 



one of the cartilaginous nodules (ptg. 3). 



In the caudal fin (Fig. 869) the dermal rays 



(D.F.R.) are similarly seated on the broad 



haemal arches of the posterior caudal verte- 



brae. The second dorsal or adipose fin has, 



as already noticed , no bony support. 



The shoulder-girdle (Fig. 874), like the skull, 



consists of a primary shoulder-girdle, homo- 



logous with that of a Dog-fish, and of several 



investing bones. The primary shoulder- 



girdle in the young fish is formed of distinct 



right and left bars of cartilage, which do not 



unite with one another ventrally. In the 



adult each bar is ossified by three bones, a 



7 tcirv-n \ i 'i n j-u 



SCapUM (SCP.), Situated ClOrsally to the 



glenoid facets, and developed partly as a 

 replacing, partly as an investing bone ; a 



. ,' i __ \ 7 . , V, 



coracoid (COR.), situated ventrally to the 

 glenoid facet, and a meso-coracoid (MS. 



I1F.R 



PTG.1 



FIG. 873. Salmo fario. 



A dermal fin-ray with its 



pterygiophore unter- 



spmous bone); PTG. 2, 



middle pterygiophore; 



