DISSECTION OF THE UPPER EXTREMITY 65 



to the vessels and nerves beneath. The coracoclavicular fascia 

 is now exposed. What are its attachments? How does it form 

 a sheath for the M. subclavius ? Divide the anterior layer of the 

 sheath transversely close to the clavicle and expose the M. sub- 

 clavius ; observe the N. subclavius entering the deep surface of 

 the latter ; with the handle of the scalpel demonstrate the attach- 

 ment of the posterior layer of the sheath behind the muscle. 

 The portion of the fascia extending between the clavicle and the 

 M. pectoralis minor is often called the " costocoracoid mem- 

 brane. ' ' Piercing this portion of the fascia find the following : 



(a) Acromiothoracic artery (A. acromiothoracalis) (0. T. thoracic axis). 



(aa) Acromial ramus (ramus acromialis) . 



(ab) Acromial network (rete acromiale). 



(ac) Deltoid ramus (E. deltoideus) (0. T. humeral branch). 



(ad) Pectoral rami (Rr. pectorales). 



(b) Acromiothoracic vein (V. acromiothoracalis}. 



(c) Cephalic vein (V. cephalica). 



(d) Lateral anterior thoracic nerve (N. thoracalis anterior lateralis). 



Divide the pars sternocostalis of the M. pectoralis major 

 about its middle and reflect it lateralward and medialward. Pre- 

 serve the branches of the anterior thoracic nerves entering the 

 deep surface of the muscle ; some of them have already passed 

 through the M. pectoralis minor. 



Note that the sheath of the M. pectoralis minor is formed 

 by a splitting of the fascia coracoclavicularis and that the fascia 

 is continued from the lower margin of the muscle to become 

 continuous with the fascia axillaris. 



Smaller Pectoral Muscle (M. pectoralis minor). 



Clean the external surface of the muscle by removing the an- 

 terior layer of the investing fascia. Examine carefully its form, 

 position, origin, insertion, action, and innervation, but do not 

 reflect the muscle until later. 



Axillary Blood-vessels. 



Remove the so-called costocoracoid membrane, viz., that 

 portion of the fascia coracoclavicularis which extends between 

 the clavicle and the upper border of the M. pectoralis minor. 

 The fossa axillaris may now be entered from above. Remove 

 any visible areolar tissue and fat and study carefully in this 

 situation the relations of the axillary artery and vein to one 

 another and to the large bundle of nerves. Note that all are 



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