306 SHOULDER-GIRDLE IN MONOTKEMES, 



Relations. At its origin from the vertebral border of the 

 scapula the muscle is intimately related to, and covered by, the 

 scapular part of the deltoid, while anteriorly the acromial part of 

 the deltoid arises close to it. The teres minor, long head of 

 triceps, and the anterior border of the subscapularis arise close to 

 it posteriorly. As the muscle leaves the acromion the supra- 

 spinatus comes into intimate relation with it, and as it runs to its 

 nsertion it courses over the capsular ligament and hides from 

 view the origin of the teres minor. 



Ornithorhynchus. (Fig. 8, /. *S'.). 



Origin. The infraspinatus arises from a concave space on 

 the external face of the scapula. This space is bounded dorsally 

 by tlie origin of the scapular deltoid from the anterior part of the 

 vertebral border and upper part of the spine of the scapula ; 

 anteriorly by the lower one-third of the spine, posteriorly by the 

 anterior border of the origin of the subscapularis, and upper half 

 of the glenoid ridge with the origin of the long head of the triceps ; 

 the more ventral convex portion of the external face of the scapula 

 does not, however, give origin to this muscle. 



Insertion. Arising by fleshy fibres the muscle runs down- 

 wards and outwards, and becoming narrower as it approaches its 

 insertion, it sinks under cover of the clavicular deltoid, and 

 winding over the capsular ligament of the shoulder joint, it is 

 inserted chiefly by tendon on the inner portion of the ventral 

 surface of the greater tuberosity, and by a few fleshy fibres on a 

 small area of the posterior surface of the humerus, immediately 

 internal to the proximal end of the delto-pectoral ridge, the inser- 

 tion being placed between the insertions of the epicoraco-humeral 

 and the supraspinatus. 



Innervation (vide j^ost, supraspinatus). 



Echidna. 

 Westling describes the origin "from the dorsal face of the 

 scapula close to the spine (the anterior border), between the 

 deltoid ii, and the subscapularis and triceps." In remarking on 



