HEAD AND NECK OF THE HORSE 25 



weaker. The fibres composing the pars cervicalis are attached to 

 the occipital part of the ligament and to the spinous processes of 

 the second and third thoracic vertebrie. Passing in a cranial and 

 ventral direction with a varying degree of obliquity, they join the 

 spinous processes of the last six cervical and the first thoracic 

 vertebrae. 



Dissection. — In order that the head and neck may be detached from 

 the rest of the body, a preliminary examination of the longus colli 

 muscle and the vertebral vessels should now be made. To expose the 

 vertebral artery and vein the last two or three intertransverse muscles 

 must be removed. 



At the present time no attempt should be made to follow the entire 

 course of the vertebral artery, or to disclose the final insertion of the 

 longus colli muscle. 



M. LONGUS COLLI. — This muscle is divisible into two parts and 

 one of them belongs to the thorax, but it is well that the dissector 

 of the neck should examine the whole of the muscle. 



(1) Pars thoracalis. — The thoracic part arises from tlie lateral 

 surface of the bodies of the first five or six thoracic vertebra?, and 

 is inserted by tendon into the transverse processes of the last two 

 cervical vertebra-. A synovial bursa is generally present between 

 the tendon and the junction of the last cervical and first thoracic 

 vertebrae. 



(2) Pars cervicalis. — The cervical part of the longus colli consists 

 of bundles of fibres taking origin from the transverse processes and 

 bodies of the seventh, sixth, fifth, fourth and third cervical vertebra?. 

 Each bundle passes in an oblique medial and cranial direction to be 

 inserted into the mid-ventral ridge of the vertebra preceding that 

 from which it arose. Sometimes the fibres pass over an entire 

 vertebra before finding insertion. The final insertion to the ventral 

 tubercle of the atlas can best be displayed at a later stage of the 

 dissection. 



A. VERTEBRALis. — The vertebral artery begins within the thorax 

 as a branch of the subclavian. It leaves the chest medial to the 

 scalenus muscle, passes ventral to the transverse process of the 

 seventh cervical vertebra, and enters the transverse foramen of the 

 sixth vertebra. It traverses the transverse foramina of the cervical 

 vertebrae up to and including the second, and ends by anastomosing 

 with a branch of the occipital artery. 



Between neighbouring transverse processes, the artery lies on the 

 vertebra? underneath the intertransverse muscles. In its course up 

 the neck it furnishes spinal and muscular branches. Rami spinales 

 enter the intervertebral foramina and anastomose with the ventral 



