The rhomboideus (a,fig. 256) is not attached to the ridge of the spine, but extends along the superior edge of the scapula ; the trapezins covers the scapula and has no clavicular pro longation.
The levator scapulee (1), fig. 256) is attached to the broad transverse process of the first vertebra, and spreads itself over all the ex ternal surface of the scapula.
The rest of the anterior member is com posed of the humerus, the radius, the carpus, the metacarpus, and the phalanges.
In the Dugong the humerus (t, fig. 246) is much shorter and thicker than in the Ma natee, and the deltoid ridge is more prominent. In the true Cetacea the humerus is always very short. In the Whalebone Whale (B, fig. 255) its length is scarcely double its breadth ; its head is hemispherical and almost parallel to the axis of the bone. The lower extremity is divided into two planes slightly inclined for the ulna and radius.
The cubitus and the radius (v) are also very short, and are anchylosed (u,fig. 246) together at both extremities in the Manatee and the Dugong, but they retain in these Cetaceans the rounded form which is peculiar to them in the other Mammalia. In the spouting Ceta ceans they are compressed, and are united by means of fibro-cartilage with the humerus and the carpus. The olecranon varies in size. In the great Whale it rises in but a small de gree, while in the Spermaceti Whale it is de veloped in the form of a hook. The radius (C, fig. 255), which is broader than the ulna (D, fig. 255), is dilated at its lower ex tremity.
The bones of the carpus are very much flattened, and of an hexagonal form ; they are less in number than in Man, but the number varies according to the species. The Manatee has six, the pisiform being wanting. The Dugong has four (w, .fig. 246), of which two are in the first row corresponding respectively to the radius and ulna, and two in the second row, the external one supporting the metacar pal bones of the pollex and index, the internal bone supporting the medius and annularis; the ulnar or little digit is supported by the uluar carpal bones of both the first and second row. The pollex (x,fig. 246) is reduced, as in the Manatee, to a small pointed meta carpal bone. The common Dolphin bas only five metacarpal bones; the Whale has seven : of' these four are in the first row, and three in the second (E, fig. 255). The metacarpals (F, fig. 255) are five in number, much flat tened, and have the general form of phalanges. The phalanges in the Zoophagous Cetaceans partake of the flattened form of the bones of the metacarpus. Their number increases in
each finger, comparatively with the normal number, sometimes very much so ; and in many cases there are some which remain cartilaginous. The pollex (G 1, fig. 255) in the great Whale has two bones; the index (2) four, the digitus medius (3) five, the annu laris (4) four, and the digitus parvus (5) three bones ; all are terminated by a cartilaginous dilatation : they form collectively a large and short paddle, obliquely rounded.
The muscles which characterize the arm of the Mammalia exist generally also in the Dolphin, and doubtless in the other Cetaceans, but with modifications which have not been so satisfactorily described as could be wished. The great pectoral muscle (a part of which is seen at g, .fig. 256) presents the sternal portion, which is called the musculus communis, or mus cle common to the two arms. The latis simus dorsi (j; fi,g.256) is represented by a little muscle, the digitations of which are attached to the ribs ; the supra-spinatus and infra spinatus are nearly of equal size, but the sub scapularis is very large. The coraco-brachialis is very short. The muscles of the other parts of the arm, that is, of the fore-arm and hand, appear in a rudimental state, and seem to exist less on account of the movements of the parts to which they are attached, than to shew the analogy of the anterior members of the Cetaceans with those of other Mammalia.
[In our dissections of tbe common Porpesse we have found the supra-spinalis of small size, corresponding to tbe size of the supra-spinal fossa. It is covered by the deltoid muscle (i). The infra-spinatus (c) is consequently of much larger size, but is a thinner muscle : behind this muscle is seen the teres major (k) and min Or (O.] As we have already said, the posterior extre mities are wanting ; all that remains of them are the rudiments of a pelvis. These rudiments are found in the Dugong to be composed of two pairs of bones (y, jig. 246) united two and two, and end to end by a cartilage, and attached by a carti lage also to one of the vertebra. In the Dolphins they con sist of two little, long, thin bones which are lodged in the flesh, one to the right and the other to the left of the anus. In the Whales, at the extremity of each of these bones (a,a, fig 257),which are reg,arded as ilia, a second (b) is found articulated, smaller, and curved ; the con vexity of which is external, and might represent a pubis, or an ischion ; it seems to correspond to the second ofthese bones in the Dugong.