MUSCLES OF THE BACK. 199 



First Layer. 



Dissection. The muscles of this layer are to be dissected by making 

 an incision along the middle line of the back, from the tubercle on the 

 occipital bone to the coccyx. From the upper point of this incision carry 

 a second along the side of the neck, to the middle of the clavicle. Infe- 

 riorly, an incision must be made from the extremity of the sacrum, along 

 the crest of the ileum, to about its middle. For the convenience of dis- 

 section, a fourth may be carried from the middle of the spine to the aero 

 mion process. The integument and superficial fascia, together, are to be 

 dissected off the muscles, in the course of their fibres, over the whole of 

 this region. 



The TRAPEZIUS muscle (trapezium, a quadrangle with unequal sides) 

 arises from the superior curved line of the occipital bone, from the liga- 

 mentum nuchaB, supra-spinous ligament, and spinous processes of the last 

 cervical and all the dorsal vertebrae. The fibres converge from these 

 various points, and are inserted into the scapular third of the clavicle, the 

 acromion process, and the whole length of the upper border of the spine 

 of the scapula. The inferior fibres become tendinous near the scapula, 

 and glide over the triangular surface at the posterior extremity of its spine, 

 upon a bursa mucosa. When the trapezius is dissected on both sides, 

 the two muscles resemble a trapezium, or diamond-shaped quadrangle, on 

 the posterior part of the shoulders : hence the muscle was formerly named 

 cucullaris (cucullus, a monk's cowl). The cervical and upper part of the 

 dorsal portion of the muscle is tendinous at its origin, and forms, with the 

 muscle of the opposite side, a kind of tendinous ellipse. 



Relations. By its superficial surface, with the integument and super- 

 ficial fascia, to which it is closely adherent by its cervical portion, loosely 

 by its dorsal portion. By its deep surface, from above downwards, with 

 the complexus, splenius, levat<y anguli scapulae, supra- spinatus, a small 

 portion of the serratus posticus superior, rhomboideus minor, rhomboideus 

 major, intervertebral aponeurosis which separates it from the erector 

 spinae, and with the latissimus dorsi. The anterior border of the cervical 

 portion of this muscle forms the posterior boundary of the posterior tri- 

 angle of the neck. The clavicular insertion of the muscle sometimes ad- 

 vances to the middle of the clavicle, or as far as the outer border of the 

 sterno-mastoid, and occasionally it has been seen to overlap the latter. 

 This is a point of much importance to be borne in mind in the operation 

 for ligature of the subclavian artery. The spinal accessory nerve passes 

 beneath the anterior border, near to the clavicle, previously to its distribu 

 tion to the muscle. 



The ligamentum nuchce is a thin cellulo-fibrous layer extended from the 

 tubercle and spine of the occipital bone, to the spinous process of the 

 seventh cervical vertebra, where it is continuous with the supra-spinous 

 ligament. It is connected with the spinous processes of the rest of the 

 cervi??il verteorae, w r ith the exception of the atlas, by means of a small 

 fibrous slip which is sent off by each. It is the analogue of an important 

 elastic ligament in animals. 



The LATISSIMUS DORSI muscle covers the whole of the lower part of f he 

 back and loins. It arises from the spinous processes of the seven inferior 

 dorsal vertebra?, from all the lumbar and sacral spinous processes, from t.h- 

 posterior third of the crest of the ilium, and from the three lower ribs ; the 



