262 THE SHOULDER GIRDLE. [CHAP. 



the Bandicoots (Peramelidce). It has always a "mesosca- 

 pular segment" as its outer end, and a "precoracoid seg- 

 ment " at its sternal end ; these are, however, not ossified. 

 Most generally it is attached to the acromion by a rather 

 strong ligament, but in the Wombat by a synovial articu- 

 lation. It is usually connected to the presternum by omo- 

 sternal cartilages of varying length, best developed in the 

 Didelphidce. 



The shoulder girdle of the MONOTREMATA (see Figs. 84 and 

 85) differs widely, in many points, from that of any other 

 Mammal, and far more resembles that of the Lizards. 



The scapula is rather long and narrow, and (especially in 

 the Ornithorhynchus) curved backwards and pointed, sickle- 

 like, at its upper end. Instead of three it presents but two 

 distinct borders and two surfaces ; but the more convex 

 border (s\ which is turned forwards and outwards in its 

 natural position, has a small projection (a] near its lower 

 end, which affords attachment to the clavicle, and is evidently 

 the acromion ; and the whole border may be considered to 

 represent the spine. Following the indications afforded by 

 the attachment of the muscles, it appears probable that the 

 whole inner surface represents the prescapular fossa of the 

 ordinary Mammalian scapula, and that the anterior portion 

 of the outer surface (pf) is the postcapular fossa, and the 

 posterior portion of the same surface (ssf) the subscapular 

 fossa, these two being divided below by a slight ridge (gfr), 

 which runs to the edge of the glenoid cavity, and from which 

 the long head of the triceps muscle takes origin. This 

 ridge then answers to the posterior or glenoid border of the 

 ordinary Mammal, and the hinder border of the Monotreme's 

 scapula (d?) would correspond to the anterior or coracoid 

 border. If this is really the case, the scapula of the Mono- 

 treme and that of the Cetacean offer the widest contrast. 



