148 ORIGIN, INSERTION, AND USE 



DORSAL REGION. 



These muscles are connected with the vertebras of the back, 



LONGISSIMUS DORSI. 



Origin. — From the six posterior dorsal spines, and by 

 lumbar fascia, and from the crest of the ileum. 



Insertion. — Into the posterior angles of the ribs, viz., the 

 twelve last ribs, and three or four hindermost cervical vertebrae, 

 and all the dorsal. 



Use. — The motions of the back and loins are mainly 

 produced by it. It is a principal agent in kicking and rearing. 



SPINALIS DORSI, AND SEMI-SPINALIS DORSI. 



These muscles are both inserted into the dorsal spines ; the 

 former is also attached to three or four posterior cervical. 



Use. — To writhe the back, or bend the withers; to in- 

 cline the spines backward, and to cooperate with the longis- 

 simus dorsi. 



LEVATORES COSTARUM. 



These are prominent bundles of fibres, which take a simi- 

 lar course to the intercostalis externi. 



Use. — They assist the intercostalis, and contribute to the 

 elevation of the ribs. 



LUMBAR REGION. 



SEMI-SPINALIS LUMBORUM. 



These are similarly distributed in the loins, to what those 

 of the semi-spinalis dorsi are in the back. 



INTERTRANSVERSALES LUMBORUM. 



These run from the edge of one transverse process to that 

 of the next. 



Use. — To approximate these processes. 



SACRO-LUMBALIS. 



They traverse the under surface of the loins. 



