1048 



SCANDINAVIAN FISllKS. 



of the <irl»it. ;iii(l is liciicc kuDwn ms the ixiMorhiful scute 

 i/ittili). Behind each s(|u:iiiii)s:il |>hite we sometimes find 

 fwi) ])lates, sometimes only oni ', touching the outer 

 sides of the pariettil, occipitjil, ;ind first dorsal scutes. 

 Where the [)lates iire two in iiunibei', the anterior is 

 evidently homologous with I lie mastoid of the 'I'eleosts 

 ()iiast(>i(l sriiii'. nit), and the posterior, which has re- 

 ceived the name of the IriHjioidl scute {fp), is the uiJi)er- 

 most plate in the curved row co\eriiig the se;ipular arch 

 of each side. It rests on (covers) a backward prolonga- 

 tion of the mastoid angle of the chondrocraniura, ju.st 

 as tlie first dorsal scute is jdaced on a similar process 

 springing from the supraoccipital jiart of the chondro- 

 cranium. We have already mentioned (p. 635) Parker's 

 comparative investigations wherein he traced the homo- 

 logues (jf the human clavicle in different vertebrates 

 from the very stage where they are mere dermal growths 



even in its cloven form, with t!ie posttcmporal b(»ne of 

 the Teleosts. It stands out. howc\ er with ecjual dis- 

 tinctness as the first plate in the np]ier lateral row of 

 bo(h- bui'klers, and forms tiic supcrioi' part of the hind 

 limit of tlie In-anchial cavitw but lies as a tegumentary 

 botic on two cartilages, one of which {the upper) is 

 the top of the above-mentioned process issuing from 

 the mastoid |)art of the head, while the other (fig. 287, 

 .s.sr) is the uppermost, segmented part of the shoulder- 

 girdle proper, a part wdiich has disappeared in the 

 Teleosts, where the dermal plate has also lieen trans- 

 formed into a portion of the endoskeleton. The median 

 pai-t of the hind limit of the branchial cavity consists 

 chiefly, sometimes entirely, of a large jdate, tlie davi- 

 (udai' sriite (cl), answei"ing to the clavicle of the Tele- 

 osts. Often, however, there is inserted, close behind 

 the upper part of this plate, a smaller one, the siipra- 



I'Mg. 287. Left scapular sculcs and cartilages of a Sturgeon (Acipenser utiirio). ' , nf tin- natural size. .4, seen frnni within: 7>. from witliout. 



.\fter Parker. 



The cartilaginous parts of the shoulder apparatus are: ssc, pars suprascapularis '' ; sc, paiv scapidans; cr, pars coraroidea: ecr, pars epicora- 



coidea; per, pars prcecoracoidea; fnc, fenestra coracoidea; /. cs, fenestra eoraco-scaptdaris. The scales (plates) transformed into tegumentary 



bones for the shonlder-ginlle are: ptp. postteniporal scute: cl. clavicular scute; id. interclavicular scute; scl. supraclavicular scute. 



(flsh-scales); and it was principally from the Sturgeon ! dariciilar (set), corresponding to the supraclavicle of 



that he traced his comjiarisons. On the outer and the Teleosts. The lower ])art of the clavicular scute 



posterior sides of the temjioral scute, or in the same curves inwards, over the ventral side, but the greater 



relative position to the mastoid scute, when this is ; part of the eNternal scapular arch on each side consists 



confluent with the former, lies a vertical plate, more 

 or less deeply forked above, cm which Parker con- 

 ferred the name of the jxisffeniponil scute (figs. 280 



at this point of the interctaricular scitte (id), the horao- 

 logue of the interclavicle remarked above among the 

 characters of the Hemibranchs. The inner parts of 



and 287, ptp), and whicii is evidently homologous, ! these plates are jjcrfect lio 



and 



in tlie Teleo.sts, 



" Tliis variation too may Ih' obscrvCjcl within tlic limits of the same species, for c'xample in the common Sturgeon. 

 '■ Above the suprascapular part, below the top of the postteniporal i.l.-ite (ptp). lies the tip of the prolongatcrl mastoid cartilage, 

 not shown in the tigure. 



