DISSECTION OF THE BACK. 



relations ; 



action ; 



in rotation 

 of bone. 



Division 

 of the 

 trape/ius : 



inner part 

 reflected ; 



outer part 

 reflected. 



Spinal 

 accessory 

 nerve in 

 trapezius. 



Clean parts 



pan 



th : 



beneath the 

 clavicle ; 



of the spine of the scapula as far as an inch from the root of thai 

 process, as well as into a rough prominence on the lower margin of 

 the spine near the inner end (fig. 12, p. 32). 



The muscle is subcutaneous. The lowest fleshy fibres end in a 

 small triangular tendon, which glides over the smooth surface at 

 the root of the spine of the scapula. The upper edge forms the 

 hinder boundary of the posterior triangular space of the neck. By 

 its insertion the trapezius corresponds with the origin of the deltoid 

 muscle, which covers the shoulder. 



Action. If all the fibres of the muscle act, the scapula gliding 

 on the ribs is moved upwards and towards the spinal column ; but 

 the upper fibres can assist other muscles in elevating, and the lower 

 fibres will help in depressing that bone. 



When the scapula is prevented from gliding on the ribs, the 

 trapezius imparts a rotatory movement to it by raising the acromion, 

 and thereby assists in raising the arm above the horizontal when it 

 has been brought up to that position away from the body by other 

 muscles. 



Dissection. The dissectors of the head and neck and upper 

 limb will now in their different parts divide the trapezius muscle 

 vertically about two inches from its vertebral attachment, and tin- 

 parts will be reflected inwards and outwards respectively. The 

 inner portion is thin, and after it has been turned up the ligamentum 

 nuchse from which it arises in the middle line of the neck will be 

 brought into view. 



The LIGAMENTUM NUCHSE is a fibrous band, which extends from 

 the spinous process of the seventh cervical vertebra to the external 

 occipital protuberance. From its deep surface a thin lamina of 

 fibres is sent forwards to be attached to the external occipital crest 

 and to the spines of the cervical vertebrae above the seventh, and 

 thereby a median partition between the muscles of the two sides 

 of the neck is formed. 



Dissection. The stout outer part of the trapezius should he 

 carefully reflected, and in the somewhat tough subjacent tissue 

 a large nerve the spinal accessory will be found running down- 

 wards and outwards from the neck on to the deep surface of the 

 muscle. More or less parallel with the spinal accessory, but below 

 it, two smaller nerves, from the third and fourth cervical, will then 

 be made out. Branches of the superficial cervical artery will also 

 be seen entering the muscle in the same neighbourhood. 



The SPINAL ACCESSORY NERVE (the eleventh cranial), having 

 crossed the posterior triangle of the neck, passes beneath the 

 trapezius, and forms a plexiform union with the branches of the 

 third and fourth nerves of the cervical plexus. The nerve can be 

 followed nearly to the lower border of the muscle. 



Dissection. The parts covered by the trapezius will next be cleaned. 



The dissector of the neck is responsible for displaying the struc- 

 tures which lie deeply in the neck beneath the clavicle, but the 

 worker on the upper limb will take note of them later on. The 

 parts in question are the posterior belly of the omohyoid muscle 



