380 ON THE SCAPULA IN MONOTREMES, 



restricted to an exceedingly small portion of the uone close to 

 the glenoid region and near to the root of the acromion. The 

 prescapular ridge indeed fwdes away ere it reaches the origin 

 of the supraspinatus, but its faint continuation towards the 

 coracoid passes behind the muscle, which is thus situated to its 

 acromial or mesoscapular side, as one would naturally expect. 



Immediately above (dorsad of) the origin of the small supra- 

 spinatus is the attachment of another small muscle, the omohyoid, 

 quite close to the continued prescapular line. The greater part 

 of the ' prescapular fossa ' is, however, occupied by portions of the 

 attachments of the serratus magnus and acromiotrachelien muscles, 

 which have, as it were, encroached upon the domain of the supi'a- 

 spinatus. 



The area of the 'inner' surface of the scajmla posterior to (i.e.^ 

 caudad of) the prescapular line (in Ornithorhynchus) is covered 

 by part of the subscapularis muscle, fibres of which arise from the 

 major part of it. The origin of this muscle reaches backwards to 

 the actual posterior margin of the bone, and, further, extends 

 around this upon the ' outer ' aspect. 



In Echidna the condition of the 'inner' surface of the scapula 

 as to muscular attachments is, superficially, a very different one ; 

 and it is this fact which has probably largely helped to render the 

 interpretation of the monotreme scapula more obscure. As stated 

 above, there is in Echidna no recognisable prescapular ridge 

 corresponding to that in Ornithorhynchus. At the same time, 

 the supraspinatus muscle is relatively a very much larger muscle, 

 whose origin occupies a very considerable area of the 'inner' 

 surface of the bone, viz., nearly the whole of the inferior or 

 ventral half of the surface above the glenoid region. As in 

 Ornithorhynchus^ the narrow attachment of the omohyoid muscle 

 is placed immediately dorsad of it, in this case crossing the inner 

 surface antero-posteriorly. The dorsal moiety of the surface, 

 amounting to fully one-half of the ' inner ' surface of the bone, is 

 in large part bare of actual muscular attachment ; but, dorsally, 

 the insertion of the serratus magnus occupies it and extends far 



