158 MUSCULAR SYSTEM. 



a purer element and by possessing organs more extensive, 

 and more complicated, for the aeration of their blood, have 

 their muscular system encreased in energy and strength be- 

 yond that of the fishes and amphibia, which, for the most 

 part, are organized to move by means of their vertebral 

 column, through an element nearly of the same specific 

 gravity as themselves. The rarity of the medium through 

 which most of the reptiles and higher animals move, neces- 

 sitates this increased muscular strength, and their bones 

 have an increased solidity proportioned to the greater force 

 of the muscles which are to act upon them. The progres- 

 sive motion of serpents, like that of fishes, depends upon 

 the movements of their trunk, and their muscles are disposed 

 so as to act with most effect on the sides of the vertebrae 

 and on the ribs. The deep grooves along the back, between 

 the spinous and the transverse processes on each side, 

 are occupied chiefly with the multifidus spina, the spi- 

 nales, and the semi-spinales dorsi, which inflect powerfully 

 the column to either side. Short as the distance is from one 

 spinous process to another, and between the short transverse 

 processes which support the ribs, those parts are moved se- 

 parately by strong interspinales and intertransversales mus- 

 cles. The ribs being free at their distal extremities, they 

 admit of extensive motion, and are furnished with large in- 

 tercostal muscles which partly represent the oblique and 

 transverse muscles of the abdomen in higher animals. The 

 recti muscles are divided in front by the soft cartilaginous 

 tapering extremities of the ribs, as they are by tendinous in- 

 tersections in most of the higher animals. These intercostal 

 muscles, of various lengths, some passing directly from one 

 rib to the next, and others passing over one or more ribs, to 

 have a more distant insertion, are strongest on the anterior 

 portion of the trunk, where their action is important in res- 

 piration, by compressing and expanding the respiratory sacs. 

 The large imbricated abdominal scuta, so important in the 

 progression of serpents, are moved and supported by dis- 

 tinct muscular fibres, which pass down to their fixed ex- 

 tremities. Many of the ordinary muscles of the head, as 

 seen in that of the rattle- snake (Fig. 74,) have a lengthened 

 and divided form in serpents, from the elongated form and 

 the great mobility of most of the bones of that part. An- 



