MUSCLES OF THE BACK. 405 



vertebrae of the loins; and principally tendinous from the pos- 

 terior part of the spine of the ilium. The external margin of the 

 belly is fleshy, and all the part nearest to the spine is wholly 

 tendinous below; but, higher up in the loins, it is so only on the 

 surface. The tendon is very strong, and divided into fasciculi, 

 chiefly near the spinous processes of the lumbar vertebrae. 

 From the under surface of this common belly, two heads, ten- 

 dinous and fleshy, are inserted into the inferior edge of the 

 transverse process of each lumbar vertebra, the smaller near its 

 root, and the larger near its extremity. On a level with the 

 lower rib, and, indeed, somewhat below it, a fissure occurs in 

 the muscle which divides it into two parts. 



The Longissirnus Dorsi is nearest the spine; it is inserted, by 

 small double tendons, proceeding from its internal surface, into 

 the ends of the transverse processes of all the vertebrae of the 

 back, except the first. It also, from its outer edge, sends long 

 slender tendons, by which it is inserted into the under edges of 

 all the ribs beyond their tubercles, except the two inferior. 



The Sacro-Lumbalis is inserted from its outer edge into all 

 the ribs at their angles, by long and thin tendons, which are 

 successively longer, the higher they are inserted. 



By turning over this muscle towards the ribs, from the other, 

 one may see coming from the eight lower ribs, as many slips, 

 which run into the under surface of the sacro-lumbalis ; they 

 are the Musculi Accessorii ad Sacro-Lumbalem. 



These two muscles keep the spine erect, and draw down the 

 ribs.* 



Tile Spinalis Dorsi> 



Between the ends of the spinous processes and the edge of 

 the longissimus dorsi, is a muscle almost entirely tendinous, and 

 scarcely to be distinguished from the latter, both in consequence 



* Varieties. The origin is uniform, but the insertions vary in their number. 

 Sometimes, a fasciculus commences by a tendinous beginning from the fourth 

 rib, and is inserted into the transverse process of the sixth vertebra of the neck; 

 a fasciculus from the sacro-lumbalis joins the fascia extended between the two 

 serrati, or reaches to the spleniuscolli: the two muscles are sometimes joined 

 closely by an intermediate fasciculus. 



