378 ON THE SCAPULA IN MONOTREMES, 



Giebel, however, in Bronn's ' Thier-Reich' (6) simply notices this 

 border of the bone as a straight ' anterior ' border, while, in his 

 "Zootomie aller Thierklassen," Briihl (7) not only figures it 

 merely under the latter name, but even designates the ridge 

 running dorso-ventrally on the outer aspect of the scapula of 

 Echidna as " die bei Echidna deutliche Spina " ! 



The true representative of the anterior or coracoid costa of the 

 typical mammalian scapula was identified by Owen (1) in Orni- 

 thorhynchus with a ridge running dorso-ventrally on the ' inner ' 

 aspect of the bone. Along the line of this ridge the actual 

 anterior part of the bladebone is flexed outwards so as to produce 

 a marked hollowing of the whole outer surface. Dorsally the 

 ridge begins close to the mesoscapular margin, but it inclines 

 backwards as it passes ventrally and terminates, at the inferior 

 or ventral extremity of the bone (glenoid region), near to the 

 base of the acromion. 



Except for this ridge the prescapula is totally suppressed. 

 That area of the inner surface of the bone extending from the 

 ridge in question to the free 'anterior' uiesoscapular margin 

 seems to represent that portion of the prescapular fossa which is 

 ordinarily formed by the mesoscapula. And the opposite or 

 ' outer ' aspect of this same portion of the blade forms part of 

 the wall of the postscapular fossa, giving origin to fibres of the 

 infraspinatus muscle, which extends forwards as far as the meso- 

 scapular margin. The posterior limit of the postscapular fossa is 

 indicated by a distinct ridge, to which the scapular triceps is 

 attached, and of \\hich more anon. 



It seems strange that Flower and Gadow (loc. cit.) should 

 completely ignore the well-marked jyr^scaijular ridge on the inner 

 aspect of the scapula of Platypus; especially as Owen (loc. cit.) 

 so distinctly drew attention to it as the true * anterior costa.' But 

 the omission is possibly to be explained by the fact that, in their 

 remarks on the monotreme scapula, the authors referred to seem 

 to have had regard more particularly to the structure of the 

 scapula in Echidna (vdiich alone they figure) ; and in this it is to 



