SHOULDER, ARM, FOREARM, AND HAND. 195 



lesser internal cutaneous nerve (Wrisberg's), and is distributed to the skin of the 

 inner surface of the arm. This nerve is called the intercosto-humeral nerve. It 

 comes through the second intercostal space. 



2. Examine the posterior wall (Fig. 136) and find the (i) subscapularis mus- 

 cle ; (2) teres major muscle ; (3) latissimus dorsi muscle ; (4) the three subscap- 

 ular nerves supplying these muscles. They are branches of the posterior cord 

 of the brachial plexus. 



Notice while dissecting the posterior wall of the axilla the following structures 

 shown in figure 136 : (i) The relation between the insertions of the teres major 

 and latissimus dorsi. Clean off the fascia and fat carefully, and see the lower 

 muscle crossing the higher, to be inserted above this. (2) Trace out and study 

 carefully the specific tendinous insertion of the pectoralis major. (3) Clean the 

 subscapularis muscle, notice its nerve- and blood-supply, and the relation of this 

 muscle to the insertion of the serratus magnus. 



3. Examine the Anterior Thoracic Angle. In this angle you will find the long 

 thoracic or external mammary artery. Trace its branches to the pectoral muscles, 

 the serratus magnus, the subscapularis, and the lymphatic glands. 



4. Examine the Posterior Thoracic Angle. In this you will find the long 

 thoracic nerve and the subscapular artery. Trace branches from this nerve to the 

 serratus magnus. (Fig. 132). Trace the subscapular artery to the muscles of 

 the posterior wall. Find its largest branch, leaving the axillary space by the 

 triangular space, between the teres major and minor and internal to the scapular 

 head of the triceps. 



5. Examine the External or Humeral Angle (Fig. 1 37). Find first the median 

 nerve, lying on the front of the axillary artery. Trace this nerve upward and 

 find its inner and outer heads, from the inner and outer cords of the brachial 

 plexus. 



The ulnar nerve lies to the inner side of the axillary artery. Trace this up 

 to the inner cord of the brachial plexus ; also trace it down behind the inner 

 condyle of the humerus. See where it joins company with the inferior profunda 

 artery. 



The musculo-cutaneous nerve lies to the outer side of the axillary artery. 

 You will find this nerve close to the insertion of the pectoralis minor. Trace it 

 through a hole in the coraco-brachial muscle. It is a branch of the outer cord of 

 the brachial plexus. 



The musculo- spiral nerve lies behind the axillary artery. (Fig. 137.) 

 Trace it downward and it will soon disappear between the two humeral heads of 

 the triceps muscle. It is a branch of the posterior cord of the brachial plexus. 



The circumflex nerve lies behind the axillary artery. It is a branch of the 

 posterior cord of the brachial plexus. It soon escapes to the posterior part of 

 the shoulder by the quadrangular space, with the posterior circumflex artery. 



The subscapular nerves, three in number, lie the most deeply of all the 

 nerves in this region. They are given off to the muscles that form the posterior 

 boundary of the axillary space. The nerve to the latissimus dorsi is called the 

 long subscapular. 



The anterior thoracic nerves are two in number ; they are called external 

 and internal. The internal anterior thoracic nerve is from the inner cord of the 

 brachial plexus ; it supplies the pectoralis minor. The external anterior thoracic 

 nerve is from the outer cord of the brachial plexus ; it pierces the clavi-pectoral 

 fascia and goes to the pectoralis major. The internal anterior thoracic nerve also 

 sends a branch to the pectoralis major muscle. This pierces the clavi-pectoral 

 fascia. 



The internal cutaneous and lesser internal cutaneous nerves are inter- 

 nal to the axillary artery. They must not be mistaken for the ulnar. 



