194 



ZOOLOGY 



SECT. 



the dermal rays (D.F.E.) are similarly seated on the broad haemal 

 arches of the posterior caudal vertebrae. The second dorsal or 

 adipose fin has no bony support. 



The shoulder girdle (Fig. 815), like the skull, consists of a 

 primary shoulder girdle, homologous with that of a Dog-fish, and 

 of several membrane 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 scapula (SOP.) situated dorsally 

 to the glenoid facets, and developed partly as a cartilage, partly 

 as a membrane bone ; a coracoid (COR.), situated ventrally to the 



glenoid facet, and 



a 



COR. 



mesocoracovl 

 (MS. COR.) situ- 

 ated above the 

 coracoid and an- 

 terior to the sca- 

 pula. Externally 

 to these is found 

 a very large 

 membrane bone, 

 the clavicle (CL.), 

 extending down- 

 wards under the 

 throat : its dorsal 

 end is connected 

 by means of 

 a supra-davide 

 (S. CL.} to a 

 forked bone, the 

 post-temporal (P. 

 TM.), one branch 

 of which articu- 

 lates with the 



epiotic, the other with the pterotic process. To the inner surface 

 of the clavicle are attached two flat scales of bone (P. CL'.), with 

 a slender rod-like post-clavicle (P.CL.) passing backwards and 

 downwards among the muscles. 



The structure of the pectoral fin is very simple. Articulated to 

 the posterior border of the scapula and coracoid are four dice-box 

 shaped bones, the proximal pterygiophores or radials (PTG.1), 

 followed by a row of small nodules of cartilage (ptg. 2) repre- 

 senting distal pterygiophores. The main body of the fin is 

 supported by dermal fin-rays, which resemble those of the median 

 fins, and have their forked ends seated upon the distal pterygio- 

 phores: the first ray, however, is larger than the rest, and 

 articulates directly with the scapula. 



FIG. 815. Salmo fario. Left half of shoulder-girdle and pectoral 

 fin, from the inner surface. CL. clavicle ; COR. coracoid ; D. F. R. 

 dermal fin-rays ; MS. COR. meso-coracoid ; P. CL.,P. CL'. i><>st- 

 clavicles ; PTG.1, proximal ; t>t<i.2, distal pterygiophores ; P. TM. 

 post-temporal; S. CL. supra-clavicle ; SCP. scapula. 



