68 LABORATORY MANUAL OF HUMAN ANATOMY 



The dissector of the arm next studies the 



Pars infraclavicularis. 



(a) Lateral cord (fasciculus lateralis) (0. T. outer cord). 



(aa) Musculocutaneous nerve (N. musculocutaneus) . 



(ab) Lateral or upper head of median nerve (N. medianus). 



(b) Medial cord (fasciculus medialis) (0. T. inner cord). 



(ba) Medial or lower head of median nerve (N. medianus). 



(bb) Ulnar nerve (N. ulnaris). 



(be) Medial cutaneous nerve of forearm (N. cutaneus anti- 

 brachii medialis) (0. T. internal cutaneous). 



(bd) Medial cutaneous nerve of upper arm (N. cutaneus brachii 

 medialis) (0. T. lesser internal cutaneous, or nerve of 

 Wrisberg) . 



(c) Posterior cord (fasciculus posterior). 



(ca) Axillary nerve (N. axillaris) (0. T. circumflex, really 



supraclavicular ) . 



(cb) Radial nerve (N. radialis) (0. T. musculospiral). 



In order to get a good view of the posterior cord and of the Nn. sub- 

 scapulares, the lateral and medial cords should be divided and reflected 

 downward. 



Anterior Serratus Muscle (M. serratus anterior) (O. T. Serratus 

 Magnus). 



Divide the posterior cord of the brachial plexus. Drag the 

 arm forcibly from the body so as to put the M. serratus anterior 

 on the stretch. Clean this muscle thoroughly and study carefully 

 the exact course and distribution of the N. thoracalis longus and 

 the A. thoracalis lateralis. Study the exact form, position, 

 origin, insertion, action, and innervation of the M. serratus 

 anterior. (Spalteholz, Fig. 311.) 



[When the student has completed this dissection of the ante- 

 rior thoracic region and axillary fossa and has dissected that 

 part of the back to which he is entitled, he may remove the upper 

 extremity from the body and continue the dissection at a side- 

 table. Cut through the Mm. serratus anterior, omohyoideus, 

 and latissimus dorsi, the transverse and dorsal arteries of the 

 scapula, and the Nn. suprascapularis et dorsalis scapulae.] 



REGION OF THE SHOULDER. 



Skin and Superficial Fascia. 



Place a block in the axillary fossa, and, beginning in front, 

 dissect the skin off the anterior and lateral aspects of the shoul- 

 der as far down as the insertion of the M. deltoideus. Eemove 

 no fat with the skin. In the superficial fascia find the following : 



