198 MISS JOAN B. PROCTER ON THE VARIATION 



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

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

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

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

 opposite to it is the fovea acetabzdum, a similar depression in the 

 extremitas scapidaris of the coracoid, which forms the proximal 

 wall of the glenoid cavity. 



In order that the varying proportions in the different genera 

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

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

 this scale ; in this way the comparative 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 Palaiobatrachus, the scapula was 

 shorter and more compact than in the ma,jorhyof modern genera, 

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

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



Text-fio-ure 2. 



Scapula of Palmobatrachus 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 WolterstorfF f. 



Examples. 



P.frvtschii. 

 Length of praecoracoid ... 10 10 



,, scapula 6 6'4 



Breadth of ,, (proximal) 3 3-6 



„ (distal) ... 4 4-5 



Although the size of the scapula varies in comparison with 

 the praecoracoid, its own proportions are remarkably stable. 

 WolterstorfF says of it J: " Es finden sich nur wenige vielleicht 

 nicht einmal specifische Verschiedenheiten." 



* Units of length . 



f ' Ueher fossile Frosclie, insbesondere das Genus Palceobatraclms' (Theil i. 

 1886; Theil ii. 1887). 

 X Op. cit. 



