ANTERIOK THOKACIC NEEVES. 703 



anterior muscle and the axillary artery. It continues its downward course over 

 the axillary surface of the serratus, to the slips of which it is distributed. 



There is a more or less definite relation between the roots of this nerve and the parts of the 

 serratus muscle. The first part of the muscle is innervated by the fifth nerve alone ; the second 

 part by the fifth and sixth, or the sixth alone; the third part by the sixth and seventh, 

 or the seventh nerve alone. 



N. Suprascapularis. The supra -scapular nerve arises from the back of the 

 cord formed by the fifth and sixth cervical nerves in the posterior triangle of the 

 neck. It occupies a position above the main cords of the brachial plexus, and 

 courses downwards and laterally parallel to them towards the superior margin of 

 the scapula. It passes through the scapular notch to reach the dorsum of the 

 scapula. After supplying the supra-spinatus muscle it winds round the great 

 scapular notch in company with the transverse scapular artery and terminates in 

 the infra-spinatus muscle. It also supplies articular branches to the back of the 

 shoulder-joint. 



Pars Infraclavicularis. The so-called infra-clavicular branches of the brachial 

 plexus are distributed to the chest, shoulder, arm and forearm. According to 

 their origin they are divisible into two sets an anterior set, derived from the 

 lateral and medial cords, and a posterior set, derived from the posterior cord. In 

 their distribution the same arrangement is maintained. The anterior nerves of 

 distribution, springing from the lateral and medial cords, supply the chest 

 and the front of the limb ; the posterior nerves, springing from the posterior cord, 

 supply the shoulder and the back of the limb. 



Anterior Branches. 



From the Lateral Cord. , From the Medial Cord 



Lateral anterior thoracic. Medial anterior thoracic. 



Median (lateral head). Median (medial head). 



Musculo-cutaneous. . Ulnar. 



Medial cutaneous nerve of forearm (O.T. 



internal cutaneous). 



Medial cutaneous nerve of arm (O.T. lesser 

 internal cutaneous). 



Posterior Branches. ^ 



Axillary nerve. 

 Radial nerve. 

 Two subscapular nerves. 

 Thoraco-dorsal nerve. 



NERVI THOKACALES ANTERIORES. 



The anterior thoracic nerves are two in number, lateral and medial. The 

 lateral anterior thoracic nerve arises from the lateral cord of the brachial plexus by 

 three roots from the fifth, sixth, and seventh cervical nerves. The medial 

 anterior thoracic nerve arises from the medial cord of the plexus, from the eighth 

 cervical and first thoracic nerves. They course downwards and forwards, one on 

 each side of the axillary artery, and a loop of communication is formed between them 

 in front of the artery. They are finally distributed to the pectoralis major and 

 minor muscles (Fig. 615). 



The nerves are distributed to the pectoral muscles in the following way. Two sets of 

 branches from the lateral anterior thoracic nerve pierce the costo-coracoid membrane. The 

 superior branches supply the clavicular part of the pectoralis major ; the inferior branches 

 are distributed to the superior fibres of the sternal portion of the muscle. The superior 

 branches come from the fifth and sixth cervical nerves ; the inferior branches, from the fifth, 

 sixth, and seventh nerves. The pectoralis minor is pierced by two sets of nerves the 

 superior set is derived from the loop of communication between the two anterior thoracic 

 nerves over the axillary artery ; the inferior set is derived from the medial anterior 



