BY J. T, WILSON AND W. J. S. McKAY. 383 



margin, that ridge on the ' outer ' surface of the scapula which is 

 present in both the genera, though most strikingly evident in 

 the Echidna. This ridge we have already referred to as the 

 'tricipital.' Mivart states [(5) p. 401] that it might be considered 

 to correspond to the axillary margin of the scapula of an ordinary 

 mammal. 



Owen styles the subscapularis in Ornitliorhynchus " a narrow 

 muscle" and regards it as restricted to the 'inner' surface; whilst, 

 as we have seen, Mivart and Flower regard it in Echidna as equally 

 restricted to the ' inner ' surface. We find that in both instances 

 the desciiption is inaccurate — as already indicated for Echidna — 

 and, for Ornithorhynchus, in the fact that a great part of what 

 Owen has taken for teres major arising from the hinder part of 

 the outer surface of the bone is really part of the subscapularis. 

 In the scapulae in both forms, in short, the subscapularis arises 

 from both 'inner' and 'outer' surfaces (the proportions differing 

 much in the two cases), and from the whole of the actual posterior 

 margin itself. The latter we are therefore disposed to look upon 

 as constituting morphologically a mere exaggerated ridge — perhaps 

 of the same nature as the prominent and strongly marked sub- 

 scapular ridge close to the true glenoid border of the human 

 scapula.* 



That the morphologically posterior, glenoid, or postscapular 

 border of the monotreme scapula is, as Flower believes, repre- 

 sented by the ridge upon the outer surface is testified to by its 

 relation in the way of attachment to the scapular triceps as well 

 as by its forming the true separation between the infraspinatus 



* This idea has at least been harboured by Mivart in reference to the 

 scapula of Platypus, for he holds that we may theoretically consider " that 

 there is a plate developed opposite to that separating the supra- from the 

 infraspinatus muscle, which, as it were, passes into the midst of the sub- 

 scapularis, throwing the posterior part of it to the outside and on to the 

 same surface as that occupied by the infraspinatus, while the rest of it is 

 but very slightly separated from the supraspinatus." The view of the 

 writers is simply that this theory of the nature of the posterior margin of 

 the scapula is good for both forms of monotreme scapula. 



