1048 
SCANDINAVIAN FISHES. 
of the orbit, and is hence known as the postorbital scute 
( ptob ). Behind each squamosal plate we sometimes find 
two plates, sometimes only one“, touching the outer 
sides of the parietal, occipital, and first dorsal scutes. 
Where the plates are two in number, the anterior is 
evidently homologous with the mastoid of the Teleosts 
( mastoid scute, mt ), and the posterior, which has re- 
ceived the name of the temporal scute ( tp ), is the upper- 
most plate in the curved row covering the scapular arch 
of each side. It rests on (covers) a backward prolonga- 
tion of the mastoid angle of the chondrocranium, just 
as the first dorsal scute is placed on a similar process 
springing from the supraoccipital part of the chondro- 
cranium. We have already mentioned (p. 635) Parker’s 
comparative investigations wherein lie traced the homo- 
logues of the human clavicle in different vertebrates 
from the very stage where they are mere dermal growths 
even in its cloven form, with the posttemporal bone of 
the Teleosts. It stands out, however with equal dis- 
tinctness as the first plate in the upper lateral row of 
body bucklers, and forms the superior part of the hind 
limit of the branchial cavity, but lies as a tegumentary 
bone on two cartilages, one of which (the upper) is 
the top of the above-mentioned process issuing from 
the mastoid part of the head, while the other (fig. 287, 
ssc) is the uppermost, segmented part of the shoulder- 
girdle proper, a part which has disappeared in the 
Teleosts, where the dermal plate has also been trans- 
formed into a portion of the endoskeleton. The median 
part of the hind limit of the branchial cavity consists 
chiefly, sometimes entirely, of a large plate, the clavi- 
cular scute (cl), answering to the clavicle of the Tele- 
osts. Often, however, there is inserted, close behind 
the upper part of this plate, a smaller one, the s upra - 
Fig. 287. Left scapular scutes and cartilages of a Sturgeon (Acipenser sturio). l / 2 of the natural size. A, seen front within ; B, from without. 
After Parker. 
The cartilaginous parts of the shoulder apparatus are: ssc, pars suprascapular is b ; sc, pars scapularis; cr, pars coracoidea; ecr, pars epicora- 
coidea; per, pars prcecoracoidea', fnc, fenestra coracoidea ; /. cs, fenestra coraco-scapularis. The scales (plates) transformed into tegumentary 
bones for the shoulder-girdle are: ptp , posttemporal scute; cl, clavicular scute; id, interclavicular scute; scl , supraclavicular scute. 
(fish-scales); and it was principally from the Sturgeon 
that he traced his comparisons. On the outer and 
posterior sides of the temporal scute, or in the same 
relative position to the mastoid scute, when this is 
confluent with the former, lies a vertical plate, more 
or less deeply forked above, on which Parker con- 
ferred the name of the posttemporal scute (figs. 28G 
and 287, ptp), and which is evidently homologous, 
clavicular (scl), corresponding to the supraclavicle of 
the Teleosts. The lower part of the clavicular scute 
curves inwards, over the ventral side, but the greater 
part of the external scapular arch on each side consists 
at this point of the interclavicular scute (id), the homo- 
logue of the interclavicle remarked above among the 
characters of the Hemibranchs. The inner parts of 
these plates are perfect bones, and as in the Teleosts, 
“ This variation too may be observed within the limits of the same species, for example in the common Sturgeon. 
h Above the suprascapular part, below the top of the posttemporal plate (ptp), lies the tip of the prolongated mastoid cartilage, 
not shown in the figure. 
