DISSECTION OF THE BACK 41 



the muscle. The knife must always be carried in the direction of the 

 muscular fibres : and care must be taken to leave none of the thin, filmy 

 deep fascia behind. As the direction of the fibres changes the position of 

 the arm must also be changed to keep the fibres which are being cleaned 

 on the stretch. In the case of the left trapez^^^s, the student must make 

 the incision through the fascia, along the lower margin of the muscle, and 

 work upwards to the level of the seventh cervical vertebra. In removing 

 the fascia from the trapezius, and indeed throughout the whole dissection 

 of the back, the cutaneous nerves must be carefully preserved, in order 

 that the dissector of the head and neck may have an opportunity of 

 establishing their continuity with the trunks from which they arise. 



M. Trapezius. The trapezius is a flat, triangular muscle, 

 which lies, in its entire extent, immediately subjacent to the 

 deep fascia. It has a very long origin, which extends along 

 the median plane, from the occiput above to the level of the 

 last dorsal vertebra below. It arises from (i) the medial 



FIG. 18. Upper Surface of the Right Clavicle. 



third or less of the superior nuchal line of the occipital bone 

 and the external occipital protuberance ; (2) the ligamentum 

 nuchae and the spine of the seventh cervical vertebra ; (3) the 

 tips of the spines of all the thoracic vertebrae, as well as the 

 supraspinous ligaments which bridge across the intervals 

 between them (Fig. 17). 



In the lower cervical and upper thoracic regions the tendinous fibres by 

 which the muscle arises lengthen out so as to form a flat tendon, which, 

 taken in conjunction with the corresponding aponeurosis of the opposite 

 side, exhibits an oval outline. 



As the fibres of the trapezius pass laterally they converge, 

 to gain an insertion into the two bones of the shoulder-girdle. 

 The occipital and upper cervical fibres incline downwards, and, 

 turning forwards over the shoulder, are inserted into the lateral 

 third of the posterior border of the clavicle (Fig. 1 8) ; the lower 

 cervical and upper thoracic fibres pass more or less trans- 

 versely to gain an insertion into the medial border of 



