BY J. T. WILSON AND W. J. S. McKAY, 381 



veatralwavds near both the anterior and posterior limits of the 

 surface. As in Ornithorhynchus, the acromiotrachelien has an 

 attachment close to the mesoscapular margin in front (cephalad) 

 of the supraspinatus, and just ventral to the serratus magnus. 



Thus it would almost appear as if nearly, if not quite, the entire 

 'inner' surface of the scapula in Echidna answered to that area in 

 Omiiliorhynclius included between the mesoscapular margin and 

 the prescapular ridge, the suhscapularis area of the inner surface 

 in the latter animal being thus unrepresented. But this is not abso- 

 lutely the case. For even in Echidna there is a narrow strip (as 

 much as 3 mm. wide) of this same inner surface close to the actual 

 posterior margin which is occupied by fibres of the suhscapularis, 

 though the major part of this muscle arises from the opposite 

 ('outer') aspect of the bone. Plainly this posterior narrow 

 subscapular strip of the inner surface corresponds to the broad 

 subscapularis area of the ' inner ' surface of the Platypus scapula 

 which lies caudad of the prescapular ridge. We do not hold that 

 it is necessary to suppose that the mere line of limitation between 

 subscapularis on the one hand and supraspinatus on the other is 

 the actual site of the morphological anterior border (prescapular 

 ridge), but we do hold that either this is the case or, as is perhaps 

 more likely, the absolute suppression in Echidna of any ridge 

 marking the anterior costa has allowed of an encroachment by 

 the supraspinatus upon the adjacent subscapularis area. 



Flower (4), indeed, probably following Mivart [(5) p. 384], 

 seems to imagine that the subscapularis in Echidna arises entirely 

 from the 'outer' aspect of the scapula, and that it is limited behind 

 by the posterior margin of the bone. Westling (9) also adopts 

 this view. 



Thus Mivart [(5) p. 398] states that in Echidna "the supra- 

 spinatus fossa is on the internal costal surface of the bone, and 

 the infraspinatus is immediately behind its actual anterior margin. 

 But," he continues, "while in Ornithorhynchus the subscapularis 

 occupies that part of the internal or costal surface of the scapula 

 which is not occupied by the supraspinatus, in the Echidna, on 



