‘ ‘ 
THE ANTERIOR THORACIC NERVES. 583 
There is a more or less definite relation between the roots of this nerve and the parts of the 
serratus magnus. 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. 
The suprascapular nerve (n. suprascapularis) 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 outwards parallel to them towards the superior border of 
the scapula. It passes through the suprascapular foramen to reach the dorsum of 
the scapula. After supplying the supraspinatus muscle it winds round the great 
scapular notch in company with the suprascapular artery and terminates in the 
infraspinatus muscle. It also supplies articular branches to the back of the 
shoulder joint. 
Infra-clavicular Nerves.—The so-called infra-clavicular branches of the brachial 
plexus are distributed to the chest, shoulder, and arm. According to their origin 
they are divisible into two sets—an anterior set, derived from the outer and inner 
cords, and a posterior set, derived from the posterior cord. In their distribution 
the same division is maintained. The anterior 
nerves of distribution, springing from the outer and 
inner cords, supply generally 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. 
: Nerves from the outer cord. 
External anterior thoracic. Outer head of median. 
Musculo-cutaneous. 
Nerves from the inner cord. femal \\a O68 Inner 
Internal anterior thoracic. Ulnar. ir, Corp 
Inner head of median. Internal cutaneous. 
Lesser internal cutaneous. 
Posterior Branches. 
Nerves from the Posterior Cord. 
Circumflex. Musculo-spiral. 
Three subscapular Fic. 430.—DIAGRAM OF THE ORIGIN 
; Reap UAT. AND DISTRIBUTION OF THE NERVES 
TO THE PECTORAL MUSCLES. 
ANTERIOR THORACIC NERVES. K.A.T, External anterior thoracic nerve ; 
I.A.T, Internal anterior thoracic 
The anterior thoracic nerves (un. thoracicales nerve ; C.5, 6, 7, C.8, T.1, Nerves of 
anteriores) are t . nave Escumen ell 1 tenn the brachial plexus ; Art, Axillary 
anteriores) are two in number, external and internal. ime Cu, Clavicle-' Gon) Gale 
The external anterior thoracic nerve arises from the clavius muscle; P.M1, Pectoralis 
outer cord of the brachial plexus by three roots— minor, joined to subelavius by 
costo-coracoid membrane; P.Ma, 
from the fifth, sixth, and seventh cervical nerves. Baeteealie rasior! 
The internal anterior thoracic nerve arises from the 
inner cord of the plexus, from the eighth cervical and first thoracic nerves. Each 
courses downwards and forwards on either side of the axillary artery. A loop of 
communication is formed between them over the artery. They are finally dis- 
tributed to the pectoralis major and minor muscles (Fig. 430). | 
The nerves are distributed to the pectoral muscles in the following way :—'l'wo sets of 
branches from the external anterior thoracic nerve pierce the costo-coracoid membrane. 
The upper branches supply the clavicular part of the pectoralis major ; the lower branches 
are distributed to the upper fibres of the sternal portion of the muscle. ‘The upper 
branches come from the fifth and sixth cervical nerves; the lower branches, from the 
fifth, sixth, and seventh nerves. The pectoral’s minor is pierced by two sets of nerves—the 
upper set is derived from the loop of communication between the external and internal 
anterior thoracic nerves over the axillary artery; the lower set is derived from the 
internal anterior thoracic nerve alone. These nerves supply the pectoralis minor muscle, 
