CETACEA. 



Fig. 256. 



Muscles of the anterior fin of a Dolphin. 



a. Rhomboideus. e. Sterno-mastoideus. 



6. Levator scapulae. /. Costo-humeralis or latissimus dorsi. 



c. Infra-spinatus. g. Portion of pectoral. 



d. Humero-mastoideus. h. Splenius. 



(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, Jig. 256) presents the sternal portion, 

 which is called the vnusculus communifi^or mus- 

 cle common to the two arms. The latis- 



571 



attached by a carti- 

 lage also to one of 

 the vertebrae. 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 regarded as ilia, 

 a second (6) 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 of these bones 

 in the Dugong. 



We perceive that 

 the internal construc- 

 tion of the organs of 

 movement in the Ce- 

 taceans does not vary 

 in the different spe- 

 cies except by mo- 

 difications the im- 

 portance of which 

 we are not able to 

 appreciate. The dif- 

 ferences in their 

 exterior structure, 

 moreover, do not ap- 



Pelvis of the Mysticete par to exercise any 

 Whale. influence over their 



mode of living; for 

 the chief of these consists in the Manatee 



Fig. 257. 



simus dorsi (J\fig. 256) is represented by a little having nails to the ends of its pectoral fin, 



muscle, the digitations of which are attached which correspond to the fingers, of which it 



to the ribs ; the supra-spinatus and infra- is in part composed ; and in its tail being oval 



spinatus are nearly of equal size, but the sub- instead of being extended laterally into two 



scapularis is very large. The coraco-brachialis wings. 



is very short. The muscles of the other parts We have in no way considered as forming 

 of the arm, that is, of the fore-arm and hand, part of the organs of movement, the protu- 

 appear in a rudimental state, and seem to berances which are seen upon the back of 

 exist less on account of the movements of the some species of spouting Cetaceans, some- 

 parts to which they are attached, than to shew times in the form of a hump, and sometimes 

 the analogy of the anterior members of the like a fin, more or less elevated. These pro- 

 Cetaceans with those of other Mammalia. tuberances, in fact, are nothing more than 



[In our dissections of the common Porpesse simple gibbosities, simple prolongations of the 



we have found the supra-spinalis of small size, skin, filled with dense cellular tissue and fat, 



corresponding to the size of the supra-spinal and resembling more or less a fin, but devoid 



fossa. It is covered by the deltoid muscle (z). of any independent movement, and without any 



The infra-spinatus (c} is consequently of much direct connection either with the vertebrae of 



larger size, but is a thinner muscle : behind the back or with the muscular system, 



this muscle is seen the teres major ( k ) and Digestive organs. The alimentary appa- 



minor (/).] ratus is one of those, which, in many of its 



As we have already said, the posterior extre- parts, presents the most important modifica- 



mities are wanting; all that remains of them are tions in the Cetaceous Order, 



the rudiments of a pelvis. These rudiments The three genera into which the Herbivorous 



are found in the Dugong to be composed of Cetaceans are divided, are characterized by 



two pairs of bones (y, fig. 246) united two three systems of dentition fundamentally dif- 



and two, and end to end by a cartilage, and ferent. The Manatees have molares with dou- 



2 P 2 



