THE UPPER LIMB 285 



distribution of the cutaneous nerves is at a lower level than their 

 origin. 



The cutaneous arteries which accompany the cutaneous nerves 

 of the thoracic and lumbar regions are derived from the dorsal 

 branches of the intercostal and liunbar arteries. 



Muscles. Trapezius. — This muscle is so named because, along 

 with its fellow, it presents a four-sided appearance like a table. 

 The two muscles have also a resemblance to a monk's hood or cowl ; 

 hence the name ciwullaris. 



Origin. — (i) The inner third of the superior curved line of the 

 occipital bone, and the external occipital protuberance ; (2) the 

 ligamentmn nuchae ; and (3) the spinous processes and supra- 

 spinous ligaments of the last cervical, and, as a rule, all the thoracic 

 vertebrae. The origins of the two muscles are markedly tendinous 

 between the second cer\'ical and third thoracic spines, where they 

 give rise to an elliptical area, widest opposite the sixth cer\'ical 

 spine. 



Insertion.— (i) The posterior border of the outer third of the 

 clavicle; (2) the inner border of the acromion process, and upper 

 lip of the posterior border of the spine, of the scapula ; and (3) the 

 tubercle which projects at the inner end of the upper lip of the spine 

 near the root. The lower fibres end in a special tendon which 

 glides over the triangular surface at the root of the spine, being 

 separated from it by a synovial bursa. 



Nerve- supply. — (i) The spinal accessory nerve (spinal portion), 

 and (2) branches from the cervical plexus, which are derived from 

 the anterior primary divisions of the third and fourth cervical nerves. 

 The nerves enter the deep smrface of the muscle after passing beneath 

 its anterior border a little above the clavicle, and the spinal acces- 

 sory, having become connected with the spinal nerves, can be traced 

 over nearly the whole extent of its deep surface, where it lies about 

 2 inches from the spines of the vertebrae. 



Blood-supply. — ^There is one specially-named artery, called the 

 sup>erficial cervical, which is a branch of the transverse cervical, 

 and, like the nerves, enters the deep surface of the muscle. 



The upper fibres of the muscle are directed do\^Tiwards, outwards, 

 and forwards ; the middle fibres pass more or less horizontally 

 outwards ; and the lower fibres pass upwards and outwards. 



Action. — ^The upper fibres, acting from their origin, elevate the 

 outer end of the clavicle and the point of the shoulder. Acting 

 from their insertion they extend the head and incline the neck 

 towards the same side, the face being directed towards the opposite 

 side. The middle fibres a] proximate the scapula to the spine, and 

 the lower fibres draw it downwards and inwards, both of these sets 

 of fibres also producing rotation of the bone, so as to elevate the 

 point of the shoulder. The entire muscle draws the scapula to the 

 spine, and produces a certain amoimt of rotation of the bone, the 

 point of the shoulder being raised, as in the act of shrugging the 

 ; shoulders. 



