7/8 MR. ST. GEORGE MIVART ON THE [JlUie 2/, 



clcido-mastoid. The deeper lajer of the same part of the deltoid 

 springs from the anterior part of about the sternal third of the su- 

 perficial 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. I) 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 

 claviculse 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 magnns, and levator 

 claviculse. 



The two parts of the deltoid are together inserted into the outer 

 side of the radial tuberosity of the humerus, just opposite to the in- 

 sertion of the pectoralis major, but separated from that muscle by 

 the insertion of the epicoraco-humeral. 



Infraspinatus (J) . This rather small muscle (fig. 2, I. 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 tri- 

 ceps. 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 hga- 

 mentous 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. //.) 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 nmch 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 pi. 52. fig. 2, E. II.). 



