778 MAMMALIA. 



although well adapted for taking hold of any object, are but ill calcu- 

 lated to sustain the weight of the body in an upright posture. Upon the 

 ground, indeed, the living 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 circum- 

 stances under which the Orang is ordained to live. 



(2237.) Having thus introduced the reader to the different orders of 

 Mammalia, as well as to the principal differences observable in the ar- 

 rangement 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. 



(2238.) To enumerate all the varieties that occur in the disposition 

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

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

 practicable, the details would scarcely possess much interest to the be- 

 ginner in comparative anatomy. Considered generally, indeed, the 

 muscular system of quadrupeds conforms very accurately in its arrange- 

 ment to that of the human subject ; and for the most part the same 

 names are applicable to the individual muscles, allowance 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 performance of special functions. To enume- 

 rate, 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 circumstances with which the human anatomist is already 

 familiar; nevertheless there are some points of practical importance 

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

 passed over in silence. 



(2239.) 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. 



(2240.) Another muscle of considerable anatomical interest is the 

 cutaneous muscle provided for the movements of the integument. In 

 many tribes, more especially those which, like the Hedgehog, the Echidna, 

 and the Porcupine, have the skin covered with spines, this muscle is 

 extremely developed, investing the greater part of the body with a thick 

 layer of muscular fibres, called not improperly the panniculus carnosus. 

 In Man, too, this muscle exists, but under a very different aspect, being 

 only found in certain regions of the body, where it forms numerous 

 cutaneous muscles adapted to different offices. In the neck, where it is 

 principally developed, it is called the platysma myoides : in the facial 



