ST D RGEON-FISHE S . 
1049 
in a manner that reminds us especially of the Trunk- 
fishes (see above, p. 619), both the clavicle and the 
interclavicle are continued inwards by an entire osseous 
disk, forming the posterior wall of the branchial cavity. 
Within (above) the anterior extremities of the inter- 
cdavicles, where these bones meet in the median line of 
the belly, we find, situated under the conns arteriosus , 
and forming, as it were, a special protection for the 
same, a fiat, heart-shaped bone. Its original dermal 
structure is indicated merely by a small, terete protu- 
berance, even externally visible, and it is apparently 
to be regarded from a morphological point of view as 
R 12 3 4 
Fig. 288. Left pectoral fin of a male Sturgeon (Acipenser sturio ) 
1.845 mm. long and taken at Lulea on July 18th, 1893. '/ 2 of 
the natural size. Seen from above. 
R, radiale of the first (composite) ray, answering to Gegenbaur’s 
mesopterygium; 1 — 4, the four true radialia, the last of which (4) 
answers to Gegenbaur’s metapterygium. 
representing the sternum of the higher vertebrates 
{sternal scute). 
The internal parts of the shoulder-girdle — omitting 
the already mentioned suprascapular part (s.sc) — form 
a. continuous mass of cartilage; but in adult Sturgeons 
this mass is seen to consist of three several parts, the 
same as we have seen above in Glanomorphs, Cyprino- 
morphs, and Thrissomorphs, namely an upper part, an- 
swering to the scapula (sc), a lower part, answering to 
the coracoid bone (cr), and an inner anterior part, cor- 
responding to the precoracoid (per). At the line where 
the scapula and coracoid meet (at f. cs), the pectoral 
fin is articulated, in the same manner as normally meets 
us among the Teleosts; but the articulary surface of the 
large first ray (spinous ray) glides partly on a projec- 
tion of the clavicle, an articulation that calls to mind 
the pectoral fin of the Sheatfish. In the basal structure 
of the fin we find (fig. 288) the same four radialia 
(brachial bones, 7 — 4) as in the Teleosts, increasing in 
length backwards (downwards). But these are cartila- 
ginous and divided into two joints (an inner and an 
outer row, cf. above, on the Herring, p. 951); and at 
the hind inferior margin of the fin there are several 
Fig. 289. Left ventral fin and pelvic bone of the same Sturgeon as 
in the preceding figure, th of the natural size. Seen from above. 
for , foramen obturatorium (?); mtp, metapterygium; pit, processus 
iliacus(?); pp , processus pubicus (?); 1 — 7, radialia. 
supplementary radialia, the inner ones branching off, 
however, from the outermost (hindmost) radiale, called 
by Gegenbaur the metapterygium. A similar, but still 
greater superfluity of cartilaginous radialia appears in 
the basal parts of the ventral fins (fig. 289). The num- 
ber of radialia is greater in the Sterlet than in the 
Sturgeon (fig. 289, 1 — 7), being in the former at least 
9, in the latter 7; but in the former the first three, 
in the latter the first four radialia (basalia.) articu- 
late at the proximal (inner) end with a common 
cartilage, answering to the pelvic bone of the Tele- 
