232 DISSECTION OF THE UPPER LIMB. 



Dissection. Supposing the clavicle raised by the pressing backwards 

 the arm, as before directed, the tube of fascia around the vessels will be 

 demonstrated by making a transverse cut in the costo-coracoid membrane 

 near the clavicle, so that the handle of the scalpel can be passed beneath 

 it. By raising the lower border of the subclavius this muscle will be seen 

 to be incased by fascia, which is attached to the bone both before and be- 

 hind it. 



The costo-coracoid membrane, or ligament (fig. 70), is a firm membra- 

 nous band, which receives this name from its attachment on the one side 

 to the rib, and on the other to the coracoid process of the scapula. Between 

 those points it is inserted into the clavicle, inclosing the subclavius muscle ; 

 and is joined by the piece of fascia that incases the small pectoral muscle. 

 From its strength and position it gives protection to the vessels surrounded 

 by their loose sheath. 



AVhen traced downwards it is found to descend on the axillary vessels 

 and nerves, joining externally the fascia on the coraco-brachialis muscle, 

 and blending with the sheath of the axillary vessels beneath the small 

 pectoral muscle. Its extent is not so great on the inner as on the outer side, 

 for internally it reaches but a very short distance on the axillary vein. 



The sheath of the axillary vessels and nerves, E, is derived from the 

 deep fascia of the neck, being prolonged from that on the scaleni muscles ; 

 and resembles, in its form and office, the funnel-shaped tube of membrane 

 surrounding the femoral vessels in the upper part of the thigh. It is 

 strongest near the subclavius muscle, where the costo-coracoid band joins 

 it. The anterior part of the tube is perforated by the cephalic vein (e), 

 the acromial thoracic artery (a), and the anterior thoracic nerve ( r ). 



Dissection. After the costo-coracoid membrane has been examined, 

 the remains of it are to be taken away ; and the subclavius muscle, and 

 the axillary vessels and nerves with their branches, are to be carefully 

 cleaned. 



The SUBCLAVIUS MUSCLE (fig. 70, D ) is roundish in form, and is placed 

 between the clavicle and the rib. It arises by a tendon from the first rib, 

 at the junction of the osseous and cartilaginous parts, and in front of the 

 costo-clavicular ligament. The fibres ascend obliquely, and are inserted 

 into a groove on the under surface of the clavicle, which reaches between 

 the two tubercles (internal and external) for the attachment of the costo 

 and coraco-clavicular ligaments. 



The muscle overhangs the large vessels and nerves of the limb, and is 

 inclosed, as before said, in a sheath of fascia. 



Action. It depresses the clavicle, and indirectly the scapula ; but if the 

 shoulder is fixed it elevates the first rib. 



The AXILLARY ARTERY (fig. 70) continues the subclavian trunk to the 

 upper lirnb. The part of the vessel to which this name is applied is con- 

 tained in the axilla, and extends from the lower border of the first rib to 

 the lower edge of the teres major muscle (H). 



In the axillary space its position will be marked by a line from the 

 middle of the clavicle to the inner edge of the coraco-brachialis. Its di- 

 rection will vary with the position of the limb to the trunk ; for when the 

 arm lies by the side of the body the vessel is curved, its convexity being 

 upwards ; and in proportion as the limb is removed to a right angle with 

 the chest, the artery becomes straight. In the upper part of the axilla the 

 vessel is deeply placed, but it becomes superficial as it approaches the arm. 



