154 THE ANATOMY OF THE HORSE. 



fleshy portions extending along the spine, under cover of the splenius, 

 and resting on the complexus. The fibres of the muscle arise by 

 successive slips from the transverse processes of the first two dorsal 

 vertebrae ; and, in common with the complexus, from the ai-ticular 

 processes of the last six cervical vertebrfe. The upper division of the 

 muscle is inserted, by a flat tendon common to the splenius, into the 

 mastoid crest ; the lower division terminates in a riband-like tendon, 

 common to the splenius and mastoido-humeralis, and inserted into the 

 wing of the atlas. 



Action. — Acting singly, to bend the neck laterally ; acting with 

 the opposite muscle, to extend the occipito-atlantal articulation (elevate 

 the head). 



The Complexus. This is one of the most powerful muscles of the 

 neck. It covers the lamellar portion of the ligamentum nuchse, which 

 separates the right and left muscles. It arises from the 2nd, 3rd, and 

 4th dorsal spines, in common with the splenius; from the trans-verse 

 processes of the first six or seven dorsal vertebrae ; and from the articular 

 processes of the cervical vertebrae with the exception of the first. From 

 these difierent points of origin the fibres converge towards the poll, where 

 they terminate in a tendon itiserted into the occipital bone. 



Action. — Both muscles will extend the occipito-atlantal joint (elevate 

 the head) ; the muscle of one side will, while elevating the head, turn 

 it slightly to the same side. 



Nebves. As already stated, each cervical nerve resolves itself into a 

 superior and an inferior primary branch. The superior primary branches 

 of the last six may now be found distributing nerves to the splenius, 

 trachelo-mastoideus, complexus, and semispinalis colli muscles ; and if 

 the complexus be raised from the ligamentum nuchse, other branches 

 will be found to ascend between the muscle and the ligament to be 

 distributed to the integument near the middle line. 



The muscles and other structures which lie above the cervical 

 vertebrse receive their chief blood supply from three vessels, viz., the 

 occipital, dorsal, and superior cervical arteries. The first of these gives 

 branches to the neighbourhood of the poll, but it is not to be sought at 

 present. 



The Dorsal Artery will be found distributing branches to the upper 

 part of the neck, in front of the withers. The artery has its origin 

 within the thorax, where, on the left side, it is a branch of the axillary 

 artery, and, on the right side, of the arteria innominata. It leaves the 

 chest by the upper part of the second intercostal space ; and inclining 

 backwards and upwards, it divides on the longissimus dorsi into a 

 number of branches distributed to the withers, and the neclc in front of 

 that region. These will be found ascending between the splenius and 

 complexus muscles. 



