REPTILIA. 



281 



The flexor brevis digitorum gives off a blip 

 to each of the three middle toes. 



Myology of Ophidian Reptiles. Muscles of 

 the Spine. In serpents, as might be expected, 

 the muscles of the spine are very completely 

 developed, and easy to identify. 



The spinalis dorsi arises from the lateral 

 surface of the spinous processes of the verte- 

 brae, and likewise receives tendons of rein- 

 forcement from the longissimus dorsi, which 

 spread out and are lost upon its inferior sur- 

 face ; this muscle divides itself internally into 

 as many fasciculi as there are vertebrae, each 

 fasciculus terminating in a very long tendon, 

 which runs in an aponeurotic sheath to be 

 inserted into the spinous process of the ver- 

 tebra to which it is destined. 



The longissimus dorsi arises by fleshy fibres 

 from the extremities of the articular apo- 

 physes, which here perform the office of 

 transverse processes. These slips, after 

 having become united with each other, give 

 off two sets of tendons, one of which runs 

 obliquely to assist in giving origin to the 

 spinalis dorsi ; the others descend in like 

 manner, and constitute the only tendons of 

 origin of the sacro-lumbalis, so that this mus- 

 cle cannot be said to have any direct insertion 

 upon the vertebral column. 



The sacro-lumbalis arises from the tendons 

 of the longissimus dorsi just described, and 

 divides itself externally into slips, each of 

 which is inserted by a slender tendon into 

 the posterior edge of the upper third of one 

 of the ribs. 



Under the spinalis dorsi is found the semi- 

 spinalis (transverso-spinalis), and beneath this 

 the interspinalis. 



On the inferior aspect of the vertebral 

 column there is found a muscle in all respects 

 analogous to the longus colli, except as re- 

 gards its extent, and which might be called 

 the transverso-spinalis inferior : this extends 

 from the inferior spinous process of one 

 vertebra to the transverse processes of the 

 second and third succeeding vertebrae. 



All the above six muscles exist from the 

 end of the tail as far as the head: their last 

 fasciculi, viz. those inserted into the skull, 

 although their arrangement is slightly altered, 

 cannot be considered on that account as being 

 distinct muscles. The sacro-lumbalis, more- 

 over, on arriving at the caudal region, is in- 

 serted into the transverse processes of the 

 caudal vertebrae, instead of into the ribs, so 

 that as the tail becomes attenuated these 

 muscles are blended together: neverthe- 

 less, there are always vestiges of them per- 

 ceptible. 



Muscles of the Ribs. These are the trans- 

 verso-costal muscles, arising from the trans- 

 verse processes of each vertebra, and running 

 to be inserted into the following rib, for about 

 the superior fourth of its length. 



The great lateral costal muscles which 

 cover the side of the trunk of the body, 

 arise behind the insertions of the pre- 

 ceding, each passing obliquely over four ribs, 

 to which it gives off a few fibres, is inserted 



into the fifth behind that from which it takes 

 its origin. 



Fig. 202. 



Lateral View of the Muscles which move the Ribs 

 of the Boa Constrictor. 



AA, the straight muscles of the back; B, the 

 first set of muscles, which arises from the trans- 

 verse processes of each vertebra, and is inserted into 

 the rib behind it, close to its head ; c, the second 

 set ; D D, the third set ; E, the fourth set ; F, the 

 fifth set; GO, short muscles which pass from carti- 

 lage to cartilage; HH, a set of oblique muscles, 

 which pass from the anterior side of the bony ex- 

 tremity of each rib to the posterior edge of each 

 scutum ; 1 1, muscles which pass from the ribs, near 

 their heads, obliquely backwards, to be inserted 

 into the skin at the edge of each scutum; K, 

 muscles of the scuta. (After Home. ) 



The great inferior costals take their origin 

 below the preceding, and are inserted in the 

 same manner, only their direction is more 

 longitudinal, so that they occupy a smaller 

 proportion of the length of the ribs. 



The smaller costal muscles are placed be- 

 tween the two preceding sets, and pass from 

 one rib to the next behind it. 



The intercostal muscles occupy their ordi- 

 nary position, and, as usual, are arranged in 

 two planes which decussate each other. 



In addition to the above, there exists in 

 the interior of the thorax an inferior transverso- 

 costal muscle; this arises from the angle of 

 the tubercle to which the rib is attached, and 

 running obliquely forwards, passing three ribs, 

 is inserted into the fourth a little below the 



