42 ANATOMY JX A NUTSHELL. 



rior layer of the tendon receives the attachment of the lower half of the 

 sternum and the deeper pari of the muscle from the costal cartilages. These 

 deep fibers, and particularly those of the lower costal cartilages ascend, the 

 higher turning backward successively behind the superficial and upper ones, so 

 thai the tendon appears to be twisted. The posterior layer reaches higher on 

 the humerus than the anterior one and from it an expansion is given off that 

 covers the bicipital groove and blends with the capsule of the shoulder- joint. 

 An expansion is given off, which lines the bicipital groove, from the inseriton 

 of the deeper fibers. An expansion passes downward to the fascia of the arm 

 from the lower part of tendon. This muscle is separated from the Deltoid by 

 slight interspaces in which lie the cephalic vein and the humeral branch of the 

 acromio-thoracic artery. Its border forms the anterior margin of the axilla. 



ORIGIN. — (1) The anterior surface of the sternal half of the clavicle. (2) 

 Half the breadth of the anterior surface of the sternum as far down as the 

 attachment of the cartilages of the sixth and seventh ribs. (3) Cartilages of 

 all the true ribs, excepting the first and seventh, or both, and aponeurosis of 

 the External oblique of the abdomen. (Plate XI.) 



Insertion. The fibers which arise from the the clavicle pass obliquely 

 outward and downward: those from the lower part of the sternum and cartil- 

 ages of the lower true ribs upward and outward, whilst the middle fibers pass 

 horizontally. The tendon of termination is inserted into the outer bicipital 

 ridge of the humerus. (Plate XXIII.) 



Action. Draws the arm forward and downward, also elevated the ribs 

 in forced inspiration. 



\'i.i;\ e Si ri ia . --- External and internal anterior thoracic. The nerves receive 

 filaments from all spinal nerves entering into the format ion of the brachial plexus. 



The costo-coracoid membrane is a strong fascia situated in the interval 

 between the Pectoralis minor and Subclavius muscles and protects the axillary 



els and nerves. It divides above to enclose the Subclavius muscle and its 

 two layers are attached to the clavicle, one in front of and the other behind 

 the muscle. The latter layer fuses with the deep clavicular fascia and with 

 fascia of the axilla r\ vessels. Internally, it blends with the fascia covering 

 the firsl two intercostal spaces and is also attached to the first rib, internal to 

 the < » r i - i 1 1 of the Subclavius muscle. Externally it is very thick and dense and 

 is attached to the coracoid process. This membrane is pierced by two arteries, 

 two nerves, and two veins. The superior and acromial thoracic arteries, the 

 external and internal anterior thoracic nerves, and the acromial ihoracic and 

 cephalic veins. 



Blood Supply. Internal mammary, intercostals, superior thoracic, 

 acromial thoracic, am! long thoracic. 



LESSON VIII. 

 Subclavius. (Plate XV). Des< ription.- This is a small triangular mus- 



•le placed in the interval between the clavicle ami the firsl rib. It is separated 

 from the firsl rib by the subclavian vessels and brachial plexus of nerves. Its 

 interior surface i- separated from the Pectoralis major by the costo-coracoid 

 membrane, which with the clavicle, forms an osseo-fibrous sheath in which the 





