382 ON THE SCAPULA IN MONOTREMES, 



the other hand, the subscapularis occupies exclusively the external 

 surface of the scapula." And upon the strength of this view of 

 the anatomy of Echidna Flower and Gadow accept the actual 

 posterior margin of the scapula in the monotremes as the true 

 morphological anterior costa or coracoid border."*^ 



This view seems to us to be an erroneous one. The origin of 

 the subscapularis even in Echidna not only occupies part of the 

 ' outer ' surface and the whole of the posterior border of the bone, 

 but extends round it so as to occupy the narrow strip of the 

 ' inner ' surface aforesaid. And when we turn to the scapula of 

 Platypus we find that the subscapularis area of the inner surface 

 is so great as to include the major part of that surface. These 

 considerations appear to us to vitiate a large part of Flower's 

 interpretation of the monotreme scapula, which is based upon 

 a mistaken view of the real condition in Echidna, and which 

 fails to give due weight to the condition in Ornithorhijnchus. 

 But if we are to deny the homology of the actual posterior 

 margin of the scapula to the true anterior or coracoid costa as 

 suggested by Flower, in what light are we to regard the former? 



Owen (1) simply accepts it as the "posterior margin or costa," 

 and, so far as we know, all authorities save Mivart and Flower 

 and Gadow so regard it (cf. Giebel and Briihl, loc. cit.j. Here, 

 however, we agree with Flower and differ from Owen in taking 

 as the true morphologically posterior, or glenoid, or ])ostscapular 



* In a passage on p. 402 of his Memoir (5) Mivart says of Echidna : — 

 " In that animal I find no trace of a ridge on the inside of the scapula like 

 that which, in OrnithorhynchiLs, separates the supraspinatus from the 

 subscapularis ; but the supraspinatus is, nevertheless, separated from the 

 subscapularis by a very large lamella, which throws the last-mentioned 

 muscle entirely to the outer side of the scapula, and is the only one 

 developed except that separating the supra- from the infraspinatus." 

 Thus it would appear as if Mivart also were inclined to regard the actual 

 posterior margin in Echidna as morphologically the anterior ; while in 

 Ornithorhynchus the homologue to the latter would be Owen's ' anterior 

 costa' ridge. But this theory supposes a very wide discrepancy between 

 the condition of the scapula in the two genera. 



