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Show 778 MR. ST. GEORGE MIVART ON THE [June 27, cleido-mastoid. The deeper layer of the same part of the deltoid springs from the anterior part of about the sternal third of the superficial surface of the clavicle, and just in front of the attachment of the two last-mentioned muscles, which, passing forwards, hide it. It then curves over the anterior margin of the clavicle, and passing backwards, between that bone and the epicoracoid, appears to join the first or more superficial layer. When the scapular arch is looked at from within, this layer is visible (fig. 7, D. 1) immediately above the lower (anterior) portion of the subscapularis, and nearer the observer than the omo-hyoid and sterno-cleido-mastoid muscles. (2) The upper and larger portion of the deltoid arises from the deep surface and posterior border of the clavicle for rather more than its upper third, and from the outer surface of the scapula for the whole extent between the lower part of the attachment of the levator claviculae and the hinder (or axillary) margin of the bone. It does not extend upwards to the superior margin of the cartilaginous upper portion of the scapula (fig. 2, D. 2),-that part presenting externally a space to which no muscle is attached between this upper or second portion of the deltoid, the serratus magnus, and levator claviculae. The two parts of the deltoid are together inserted into the outer side of the radial tuberosity of the humerus, just opposite to the insertion of the pectoralis major, but separated from that muscle by the insertion of the epicoraco-humeral. Infraspinatus (?). This rather small muscle (fig. 2, J. S.) arises from the outer surface of the spinous process of the scapula, and from the membrane intervening between that process and the first or upper spur of the epicoracoid; it takes origin almost down to the margin of the glenoid cavity. Thence it passes downwards in front of the long head of the triceps, and is inserted into the outer side of the humerus just below the head of the bone and between the summits of the external and internal humeral heads of the triceps. Its insertion is mainly superior to that of the latissimus dorsi, though the tendon of the latter slightly overlaps it. The infraspinatus is as it were strapped down by a strong ligamentous band, which passes from the lower part of the axillary margin of the scapula to the outside of the head of the humerus, underneath the epicoraco-humeral and above the insertion of the deltoid. The epicoraco-humeral is very largely developed, and arises from the two spurs of the epicoracoid and from the intervening membrane which closes the fenestra. It is inserted (figs. 2, 8 & 10, E. H.) into the summit of the radial tuberosity between the insertions of the pectoralis major and deltoid. It is covered externally by the lower part of the deltoid and by the pectoralis major; and its inferior margin is much connected with the adjacent part of the coraco-brachialis. This muscle appears to me to answer to that which I have called by the same name in the Echidna (Trans. Linn. Soc. vol. xxv. 1866, p. 383, and pl. 52. fig. 2, E. II). • |
