1894.] ANATOMY OF ORKITHOB,HT!TCHTJS. 697 



Owen does not mention it in this animal. Mivart says it is absent 

 in Echidna. 



Subscapularis. — There would appear to be a difference in the 

 origin of the two muscles supra-spinatus and subscapularis in the 

 two species of Monotremes. According to Mivart, in Echidna, 

 supra-spinatus occupies the whole of the costal surface of scapula, 

 while subscapularis is confined to outer surface. Owen states that 

 subscapularis is a narrow muscle in Ornithorhynchiis. It would 

 appear, rather, to be a large muscular sheet arising from the 

 so-called subscapular fossa, i. e., posterior part of outer surface, and 

 from almost the whole of the costal surface, so-called supra- 

 spinous fossa. The two parts are intimately blended, as they pass 

 beyond scapula to humerus, and are inserted together on the ulnar 

 tuberosity. In the portion of the tendon which springs from the 

 costal surface is a sesamoid bone ; the other portion is inserted 

 into the ulnar tuberosity just below the sesamoid bone. It is, 

 however, an artificial dissection to separate the two portions. 

 The larger portion, containing the sesamoid bone, would seem from 

 its insertion to represent the subscapular muscle of human 

 anatomy ; the portion arising from the so-called subscapular fossa, 

 i. e., posterior part of outer surface, would seem to represent that 

 portion of the subscapularis of human anatomy which arises close 

 to axillary border of scapula. This portion is often separate, and 

 is called in human anatomy subseapulo-capsularis by Macalister. 

 It is in Man inserted just below the chief portion of the sub- 

 scapular muscle. In this animal it is also inserted below the rest 

 of the muscle. If we imagine the axillary border of the human 

 scapula twisted backwards, so that it, together with the origin of 

 triceps, comes to occupy the middle of the bone, then this sub- 

 seapulo-capsularis would be also twisted backwards and its origin 

 would occupy the exact position which it has in OmithorhyncJms. 

 The two portions of the muscular sheet are supplied by the 

 separate branches of the same nerve which is a branch from the 

 upper part of brachial plexus. Cones describes this muscle as 

 upper part of teres major, i. e., the muscle which he speaks of as 

 arising from both sides of scapula and embracing the bone. Since, 

 however, the two portions of his teres major are quite distinct 

 from their origin to their insertion, and separated, moreover, by 

 the long head of the triceps, this would lead one to think that 

 that portion which passes to ulna tubercle is subscapularis. 



Muscles of Aem. 



Deltoid. — Consists of two parts, anterior and posterior. They 

 are both inserted into strongly marked deltoid ridge of humerus, 

 and are quite distinct to their insertion. 



Biceps. — Arises by two heads ; both are coracoid in their origin 

 and both are radial in their insertion. The larger arises from 

 sternal extremity of coracoid, the smaller arises nearer the glenoid 

 cavity from epicoracoid. They blend about the middle of the arm 



