58 THE SUPERIOR EXTREMITY 



possible, in conjunction with the dissector of the head and neck. 

 Divide the muscle about two inches from the spines of the verte- 

 brae, and throw it laterally, towards its insertion. The trapezius 

 is very thin at its origin, and the greatest care must therefore be 

 taken not to injure the subjacent rhomboid muscles. The small 

 bursa between the tendon of insertion of the lower part of the 

 trapezius and the flattened apex of the spine of the scapula must 

 not be overlooked, and the nerves and vessels on the deep surface 

 of the muscle must be cleaned and preserved. They are the 

 accessory nerve and branches of the third and fourth cervical 

 nerves, the ascending branch of the transverse cervical artery, 

 and branches of the descending branch of the transverse cervical 

 artery^ The latter pass into the trapezius from between the 

 muscles of the second layer. 



Nerves and Vessels of Supply to the Trapezius. A dis- 

 section of the deep surface of the reflected muscle will reveal 

 the following structures : 



a. The accessory nerve. 



b. Two or three nerves from the cervical plexus. 



c. The ascending branch of the transverse cervical artery. 



d. Twigs of the descending branch of the transverse cervical 



artery. 



These constitute the nervous and vascular supply of the 

 trapezius. 



The nerves have already been displayed by the dissector of 

 the head and neck, as they cross the posterior triangle of the 

 neck. The branches from the cervical plexus come from the 

 third and fourth cervical nerves. On the deep surface of the 

 trapezius they join with branches of the accessory nerve to 

 form the subtrapezial plexus, from which twigs proceed into the 

 substance of the muscle. The terminal twig of the accessory 

 nerve can be traced nearly to the lower margin of the 

 trapezius. 



The ascending branch of the transverse cervical artery, which 

 accompanies the accessory nerve, must be followed to the 

 anterior border of the trapezius, where it will be seen to 

 spring from the trunk of the artery at the point where it 

 divides into its ascending and descending branches. 



The twigs from the descending branch of the transverse 

 cervical artery pierce the muscles of the second layer or pass 

 between them, close to the vertebral border of the scapula. 



Dissection. The posterior belly of the omo-hyoid, the trans- 

 verse scapular artery, and suprascapular nerve" must now be 

 displayed, and the clavicular and scapular insertions of the 

 trapezius must be examined. Divide the trapezius into an upper 



