660 MAMMALIA. 



animal puts the spectator in mind of a human being crippled in the 

 lower extremities; but, in its native trees, these members, like those 

 of the Sloth, are admirably suited to the circumstances under which 

 the Orang is ordained to live. 



(740.) Having thus introduced the reader to the different orders 

 of Mammalia, as well as to the principal differences observable in 

 the arrangement of their osseous system, we must briefly glance at 

 some few points connected with their myology, selecting those that 

 seem most worthy of being specially pointed out to the notice of 

 the anatomical student. 



To enumerate all the varieties that occur in the disposition of 

 the muscular system in vertebrate animals, would, of course, be 

 incompatible with the extent of this work ; and perhaps, even were 

 it practicable, the details would scarcely possess much interest to 

 the beginner in comparative anatomy. Considered generally, in- 

 deed, the muscular system of quadrupeds conforms very accurately 

 in its arrangement to that of the human subject ; and for the most 

 part the same names are applicable to the individual muscles, al- 

 lowance being made for such modifications in the manner of their 

 origins and insertions as are rendered necessary by the disposition 

 of the skeleton, or in order to accommodate them to the perform- 

 ance of special functions. To enumerate, therefore, the muscles of 

 the jaws, of the neck, of the spine, of the chest, of the abdomen, 

 or even of the extremities, in such genera as have the members last 

 mentioned completely developed, would only be to repeat cir- 

 cumstances with which the human anatomist is already familiar : 

 nevertheless, there are some points of practical importance con- 

 nected with this part of our subject that must not be altogether 

 passed over in silence. 



(741.) The diaphragm is a muscle only met with in the 

 class before us, and in all Mammalia it forms the great agent in 

 respiration ; dividing the thoracic from the abdominal cavity by a 

 broad musculo-tendinous septum, and presenting a disposition in 

 all essential particulars similar to that of Man. 



(742.) Another muscle of considerable anatomical interest is 

 the cutaneous muscle provided for the movements of the inte- 

 gument. In many tribes, more especially those which, like the 

 Hedgehog, the Echidne, and the Porcupine, have the skin 

 covered with spines, this muscle is extremely developed, invest- 

 ing the greater part of the body with a thick layer of muscular 

 fibres, called not improperly the panniculus carnosus. In Man, 



