570 



CETACEA. 



In the Zoophagous Cetaceans the spine of 

 the scapula does not project much. The 

 supra-spinal fossa is reduced to a mere groove 

 in the common Dolphin, and entirely dis- 

 appears in the Gangetic species (Platanista) ; 

 the coraco'id process does not exist in this last 

 dolphin ; and the same absence is found in 

 the Biil<cnidce, whilst it is seen in the common 

 Dolphin and the Cachalot. Lastly, the acro- 

 mion appears always to exist, but with a 

 different development, in different species. 

 In the scapula of the Whalebone Whale (A, 

 jig. 255) it is marked a. The articular or 



Fig. 255. 



Bones of the anterior fin of a Whale, 

 Baleena Mysticetus. 



glenoid cavity (li) is proportionally larger in 

 this species than in the Spermaceti Whale. 

 The muscles of this part of the anterior mem- 

 ber present some remarkable modifications, but 

 with which we are only acquainted as they 

 exist in the common Dolphin. Thus the 

 serratus magnus does not extend as far as the 

 cervical vertebra, and ends at the ribs ; the 



pectoralts minor, instead of descending on the 

 ribs, is directed towards the anterior extremity 

 of the sternum. 



The rhomboideus (a, Jig. 256) is not attached 

 to the ridge of the spine, but extends along the 

 superior edge of the scapula ; the trapezius 

 covers the scapula and has no clavicular pro- 

 longation. 



The levutor scapula (b,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, Jig. 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,jig. 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, Jig. 255), which is broader than the ulna 

 (D, Jjg. 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, Jig. 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 

 ulnar carpal bones of both the first and second 

 row. The pollex (.r,fg. 246) is reduced, as 

 in the Manatee, to a small pointed meta- 

 carpal bone. The common Dolphin has only 

 five metacarpal bones ; the Whale has seven : 

 of these four are in the first row, and three in 

 the second (E, Jig. 255). The metacarpals 

 (jF, Jig. 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 I, fig. 255) 

 in the great Whale has two bones ; the index 



