THORAX AND ABDOMEN OF THE HORSE 5 



difficulty. Its fibres take origin from the transverse processes of the 

 first six thoracic vertebra.^ ; and its insertion is to the transverse 

 processes of the last four cervical vertebra'. 



M. SPINALIS (et SEMispiNALis) DORSi ET CERVicis. — The spinal 

 . muscle of the back and neck appears to be an off-shoot from the 

 longissimus dorsi with which its caudal portion is connected in the 

 most intimate fashion. Careful dissection shows that the muscle has 

 tendinous connections with the spinous processes of the lumbar and the 

 last five or six thoracic vertebrae ; but it is here that the identity of 

 the muscle is confused with that of its much larger neighbour. About 

 the eleventh or twelfth thoracic vertebra the spinal muscle begins to 

 become more independent. Its more cranial attachments are to the 

 caudal border of the first five or six thoracic spinous processes and the 

 rudimentary spinous processes of the last four or five cervical vertebrae. 



Dissection. — Remove the longissimus dorsi and spinalis muscles. In 

 doing so, observe the muscular branches of the dorsal rami of the 

 intercostal and lumbar arteries. 



M. MULTIFIDUS ^ DORSI. — A series of small muscles lie close against 

 the vertebral column. They arise from the sacrum, the articular and 

 mam miliary processes of the lumbar and the last two or three thoracic 

 vertebrae, and from the transverse processes of the other thoracic 

 vertebree. Each muscular bundle crosses from two to four spinous 

 processes in an oblique cranial and dorsal direction to its insertion 

 into the spinous process of a lumbar or thoracic vertebra. In the 

 lumbar region the insertion is close to the free end of the spinous 

 process, and this is also the case from the last to about the tenth 

 thoracic vertebra. Thereafter, however, the insertion is further and 

 further removed from the extremity of the process. 



Mm. levatores costarum. — The levators of the ribs form a .series 

 of small muscles arising from the transverse processes of the thoracic 

 vertebrae. The fibres of each muscle run in a caudal, ventral and 

 lateral direction to be inserted into the cranial border of the rib 

 succeeding the vertebra from which they have taken origin. The first 

 rib is not provided with a levator muscle. 



Mm. intertransversales lumborum. — Thin and weak inter- 

 transverse muscles, containing a considerable proportion of tendinous 

 tissue, occupy the intervals between the transverse processes of the 

 lumbar vertebrae. Generally there is no muscle between the processes 

 of the fifth and sixth vertebrae. 



^ Multifidus (from mulius, iw&uy -\- finder e, to cleave or split) [L.], cleft or divided 

 into many parts. 



