CETACEA. 



Fig. 256. 



Muscles of the anterior Jin of a Dolphin. 



a. Rhomboideus. e. Sterno-mastoideus. 



b. 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, fig. 256) presents the sternal portion, 

 which is called the musculus communis,or mus- 

 cle common to the two arms. The latis- 

 simus dorsi (f,f l g-%56} 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-brachudis 

 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 the common Porpesse 

 we have found the supra-spinalis of small size, 

 corresponding to the 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 

 minor (/).] 



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 



Fig. 257. 



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 

 anischion; it seems 

 to correspond to the 

 second of these bones 

 in the Dugong. 



We perceive that 

 the internalconslruc- 

 tion of the organs of 

 movement in the Ce- 

 taceans does nol 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- 

 pear to exercise any 

 influence over their 

 mode of living; for 



the chief of these consists in the Manatee 

 having nails to the ends of its pectoral fin, 

 which correspond to the fingers, of which it 

 is in part composed ; and in its tail being oval 

 instead of being extended laterally into two 

 wings. 



We have in no way considered as forming 

 part of the organs of movement, the protu- 

 berances which are seen upon the back of 

 some species of spouting Cetaceans, some- 

 times in the form of a hump, and sometimes 

 like a fin, more or less elevated. These pro- 

 tuberances, in fact, are nothing more than 

 simple gibbosities, simple prolongations of the 

 skin, filled with dense cellular tissue and fat, 

 and resembling more or less a fin, but devoid 

 of any independent movement, and without any 

 direct connection either with the vertebrae of 

 the back or with the muscular system. 



Digestive organs. The alimentary appa- 

 ratus is one of those, which, in many of its 

 parts, presents the most important modifica- 

 tions in the Cetaceous Order. 



The three genera into which the Herbivorous 

 Cetaceans are divided, are characterized by 

 three systems of dentition fundamentally dif- 

 ferent. The Manatees have molares with dou- 

 2 P 2 



Pelvis of the Mysticete 

 Whale. 



