198 MISS JOAN B. PROCTER ON THE VARIATION 



and the sapra-scapula will be alluded to as the shaft. A circular 

 depression is often situated in the thickness of the shaft, where 

 it becomes one with the pars glenoidalls : it is called the super- 

 ficial articulation, and forms the distal wall of the glenoid cavity ; 

 opposite to it is \\vq fovea acetahtdum^ a similar depression in the 

 extremitas sca2ndaris of the coracoid, which forms the proximal 

 wall of the glenoid cavity. 



In order that the varying proportions in the diffei^ent genera 

 may be fully appreciated, the length of the prtecoracoid will always 

 be given as 10 units*, and all other measurements standardized to 

 this scale ; in this way the compai'ative reduction and develop- 

 ment can be seen at a glance, as the normal length of the scapula 

 should be about 10 also. 



In fossil frogs of the genus Paloiohatrachus, the scapula was 

 shorter and more compact than in the majoritj^of modern genera, 

 being three- to four-fifths the length of the prfecoracoid, and about 

 once and a half as long as broad at its expanded end. The pars 



Text-fie'ure 2, 



^^^7\ 



Scapula of Pa?(So5ffifrac7iHS sp. ? X2. (After Woltevstorff.) 



acromialis was not distinct from the pars glenoidalis, but, accord- 

 ing to Wolterstorff, a groove can be seen on the inner surface of 

 the bone, in place of the cleft shown by modern forms. 



The following figures are standardized from actual measure- 

 ments given by Wolterstorfl' f- 



]^xa7npl6s. 



Length of pr^ecoracoid ... 



,, scapula , 



Breadth of ,, (proximal) 



„ „ (distal) ... 



Although the size of the scapula varies in comparison with 

 the prtecoracoid, its own proportions are remarkably stable. 

 "Wolterstorff says of itj: " Bs finden sich nur wenige vielleicht 

 nicht einmal specifische Verschiedenheiten.''' 



* Units of length. 



t ' Uebor fossile Frosclie, iusbesondere das Genus FaJmoJiatraclius' (Theil i. 

 1886; Theil ii. 1887). 

 X Oj). cit. 



