208 



ZOOLOGY 



SECT. 



S.Or 



10. 861.— Skull of young Salmon, second neekaftei hatching • 

 the mvesting bones removed. Au. auditory capsule ; B>: 1, 

 first branchial arch ; Ch. notochord ; C. Ihj. hyoid cornu ; 

 lo. fontanelle ; 0. Hv. basihyal ; H. Hij. hypohyal ; U. M. 

 hyoiiiandibular ; 1. Hy. interhyal ; (i, (2^ labial cartilages ; 

 Mck. Meckel's cartilage ; M. Ft. metapterygoid region of 

 primaiy iipper jaw ; fa. ch. parachordal ; PL PL palato- 

 pterygoid region; Qv. quadrate region; S.Or. supraorbital 

 region of cranium ; Sy. symplectic region of suspensorium ; 

 T. 0<\ cranial roof ; Tr. trabecula ; 11, optic foramen ; V, 

 trigeminal foramen. (From Parker and Bettany's Morpholor/y 

 0/ the Skull.) 



set of pterygiophores, so that the fiu-skeleton is multiserial, as in 



the Dog-fish. The 

 proximal series con- 

 sists of slender bony 

 rays — the interspin- 

 ous bones (Fig. 802, 

 PTG. 1; Fig. 865, 

 PTG.), lying in the 

 median plane, be- 

 tween 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 carti- 

 lage (j^tg. 3) forming the third series of radials. The dermal fin- 

 rays or lepidotrichia (B.F.R.), which lie in 

 the substance of the fin itself, are slender 

 bones, jointed like the antennae of an Arthro- 

 pod, and mostly branched in the sagittal 

 plane (Fig. 865, B.F.R.). Each is formed of 

 distinct right and left pieces (Fig. 862), 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. 858) 

 the dermal i-ays {D.F.R.) are similarly seated 

 on the broad ha3mal arches of the posterior 

 caudal vertebrae. The second dorsal or adi- 

 pose fin has no bony support. 



The slumlder-girdle (Fig. 863), like the 

 skull, consists of a iirimary shmdder -girdle, 

 homologous with that of a Dog-fisli, and of 

 several investing bones. The primary shoulder- 

 girdle in the young Fish is formed of dis- 

 tinct 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 sccqnda (SCP.), situated dorsally to the 



Fig. 8(i2.— Salmo fario. 

 A dermal fin-ray with its 

 supports. B.F.R. dermal 

 fln-ray;PTG.l, proxirnal 

 pterygiophore (interspin- 

 ous bone); FT6 2, middle 

 pterygiophore; yitg. 3, dis- 

 tal pterygiophore (cartila- 

 ginous). 



