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THE MUSCLES OF THE SHOULDER GIRDLE 295 
(M. cleido-mastoideus) partly overlaps the other (M. cleido-transversarius), which 
lies dorsal to it. The former is attached to the mastoid process and the occipital 
bone by a broad tendon which fuses at its terminal part with that of the splenius 
and longissimus capitis et atlantis; it is also attached to the tendon of insertion of 
the sterno-cephalicus by aponeurosis. The dorsal part is attached to the transverse 
processes by four fleshy digitations. The belly of the muscle is adherent superfi- 
cially to the cervical fascia and the cutaneous muscle, and deeply to the omo- 
hyoideus. In front of the shoulder its deep face may present a tendinous inter- 
section of variable development.! Here the muscle becomes wider, covers the 
shoulder joint, passes between the brachialis and biceps, and is inserted by means 
of a wide tendon which it shares with the superficial pectoral muscle. 
Relations.—Superficially, the skin, cervical fascia, the parotid gland, the cuta- 
neus, the brachialis, and branches of the cervical nerves; deeply, the splenius, 
longissimus capitis et atlantis, rectus capitis ventralis major, omo-hyoideus, ser- 
ratus ventralis, anterior deep pectoral and biceps muscles, the inferior cervical 
artery, the prescapular lymph glands, and branches of the cervical nerves. The ven- 
tral edge of the muscle forms the dorsal boundary of the jugular furrow. The 
dorsal border may be in contact with the cervical trapezius, or be separated from 
it by a variable interval. 
Blood-supply.—Inferior cervical, carotid, and vertebral arteries. 
Nerve-supply.—Spinal accessory, cervical, and axillary nerves. 
The pectoral fascia is a thin membrane covering the surface of the pectoral 
muscles, to which it is, for the most part, closely attached. It detaches a layer 
which passes between the superficial and deep pectorals. At the posterior edge of 
the triceps another layer is given off, which passes on the lateral surface of this 
muscle to blend with the scapular fascia; the deeper layer becomes continuous with 
the subscapular and cervical fascize. 
The pectoral muscles form a large fleshy mass which occupies the space be- 
tween the ventral part of the chest-wall and the shoulder and arm. They are 
clearly divisible into a superficial and a deep layer. The superficial layer may be 
subdivided into two parts by careful dissection; the deep layer is clearly made up 
of two muscles. 
2. Superficial pectoral muscle (M. pectoralis superficialis). 
(a) Anterior superficial pectoral muscle (pars descendens).?—This is a short, 
thick, somewhat rounded muscle, which extends from the manubrium sterni to 
the front of the arm. It forms a distinct prominence on the front of the breast, 
which is easily recognized in the living animal. 
Origin —The cariniform cartilage of the sternum. 
Insertion.—(1) The curved line of the humerus with the brachiocephalicus; (2) 
the fascia of the arm. 
Action.—To adduct and advance the limb. 
Structure —The belly of the muscle is convex on its superficial face, but deeply 
it is flattened where it overlaps the posterior superficial pectoral. Here the two 
muscles are usually closely attached to each other, and care must be exercised in 
making the separation. The tendon of insertion blends with that of the brachio- 
cephalicus and with the fascia of the arm. At the middle line of the breast a fur- 
Tow occurs between the two muscles; laterally, another furrow, containing the 
cephalic vein, lies between the muscle and the brachiocephalicus. 
Relations—Superficially, the skin, fascia, and panniculus; deeply, the pos- 
1 This is regarded as a vestige of the clavicle. On this basis the portion of the muscle from 
the vestige to the arm represents the clavicular part of the deltoid and perhaps the clavicular part 
of the pectoralis major of man. 
* Also termed the pectoralis anticus or pars clavicularis. 
