384 ON THE SCAPULA IN MONOTREMES, 



and subscapularis muscles in the scapulae of both the genera of 

 the order. 



But it is not alone in the Monobremata that a displacement of 

 the true postscapular border on to the outer surface of the scapula 

 seems to occur. In his account of the anatomy of the scapula of 

 Myrmecophaga tetradactyla in Bronn's " Klassen und Ordnungen 

 des Thier-Reichs," Giebel [(6) p. 408, pi. lxx. fig. 5] describes the 

 second or postscapular spine in the following terms : — " Ihr fast 

 parallel [to the mesoscapular spine] lauft eine zweite Grate, der 

 eigentliche Hinterrand [the italics aie ours], hinter welchem aber 

 die Platte des Schulterblattes noch betrachtlich erweitert ist." 

 And the condition here described is common to many edentate 

 forms [(6) pi. lxx. and (8) pi. xxi.-xxiii.] and is also very promi- 

 nent in the marsupial Notoryctes typhlops (10). In these cases it 

 is associated with a very great development of the scapular triceps. 

 Thus in Dasypus sexcinctiis Galton (11) describes the scapular 

 triceps as the largest part of the muscle, and as arising from the 

 " inferior or lesser spine of the scapula along the whole of its 

 extent." He also found a part attached to the actual "axillary" 

 border of the bone just posterior to the neck of the bone which 

 he opi^ied to be the representative of the human long head ; but 

 in view of all the facts, we cannot admit this to be so to the 

 exclusion of the rest of the scapular fibres. Indeed, the fact is 

 that where the postscapular spine is present the triceps is not 

 usually confined to it alone but spreads backwards upon the flat 

 surface of bone behind it as far as the actual posterior margin of 

 the bone, from which also fibres generally arise. 



This at least is the case in Notoryctes, as ascertained by one of 

 us (W.), and apparently it is so also in Chlamydophorus truncatus 

 (12), in which a postscapular spine is well developed and the 

 scapular triceps is "enormous." 



In Orycteropus cajoensis Humphry (13) simply describes a very 

 extensive origin by three divisions from the " posterior costa " ; 

 but, as in this animal the postscapular spine rises from the 

 external surface pretty close to the actual posterior border, there 

 can be no doubt that the attachment of the large muscle actually 



