319 THE MUSCULAR SYSTEM. | 
border to the costo-coracoid membrane. It crosses the axillary vessels and the 
cords of the brachial plexus, and is pierced by branches of the anterior thoracic 
nerves. 
Either in part or wholly the pectoralis minor may pass over the coracoid process of the 
scapula, separated from it by a bursa, to be inserted into the coraco-acromial ligament, or the 
acromion process ; or piercing the coraco-acromial ligament, it may be attached to the capsule of 
the shoulder joint (coraco- humeral ligament). 
Pectoralis minimus.—This is a slender slip, rarely present, which extends between the first 
costal cartilage and the coracoid process. 
The subclavius muscle arises from the upper surface of the first costal 
cartilage in front of the costo-clavicular hgament. It is inserted into a groove in 
the middle third of the under surface of the clavicle. The muscle is invested by 
the fascia which forms the costo-coracoid membrane, and is concealed by the 
clavicle and the clavicular origin of the pectoralis major. 
The sterno-clavicularis is a small separate slip, rarely present, extending beneath the 
pectoralis major from the upper part of the sternum to the clavicle. 
The serratus magnus (m. serratus anterior) is a large curved quadrilateral 
muscle occupying the side of the chest and inner wall of the axilla. It arises by 
fleshy shps from the external aspect of the 
upper eight ribs. The first shp is a double 
one, arising from the first two ribs and 
the fascia covering the intervening space. 
The insertion of the muscle is threefold. 
(1) The first portion of the muscle (from 
the first and second ribs) is directed back- 
wards to be inserted into the ventral 
aspect of the upper angle of the scapula. 
(2) The next three slips of the muscle 
(from the second, third, and fourth ribs) 
the scapula. (3) The last four slips (from 
the fifth, sixth, seventh, and eighth ribs) 
are directed obliquely upwards and back- 
wards, to be inserted on the ventral aspect 
of the lower angle of the scapula. The 
external surface of the muscle is partly 
superficial below the axilla, on the side 
wall of the chest, where its slips of origin 
are seen inter- digitating with those of the 
obliquus externus abdominis. Higher up 
it forms the inner wall of the axilla, and 
is in contact with the pectoral muscles in 
front and the subscapularis behind. Its 
upper border appears in the floor of the 
Fic. 233,—Tue Serratus Macnus Musciz. posterior triangle, and over it the axillary 
artery and the cords of the brachial plexus 
pass to reach the armpit. The lower border is oblique, and is in contact with the 
latissimus dorsi muscle. The deep surface of the muscle is in contact with the 
chest wall, so that the serratus magnus along with the subscapularis muscle 
separates the scapula from the ribs. The muscle may extend higher than usual, 
so as to be continuous with the levator anguli scapule. 
are inserted into the vertebral border of 
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