THE OSTEOLOGY OF THE DIADECTIDAE 



J 43 



outer side just posterior to the articular face, and passes forward 

 and inward to open on the inner face of the bone in the bottom of a 

 pit which also receives the opening of the coracoid foramen. In 

 this specimen the foramen opens on the lower edge of the shaft and 

 is almost within the articular space. Its position on the inner face 

 cannot be given. 



The line between the coracoid and pre- 

 coracoid cannot be distinguished. The 

 two bones extend forward and inward 

 as flat plates which terminate in a straight 

 anterior-posterior line medially. The two 

 plates of the opposite side normally joined 

 in a symphasis, but the two sides of the 

 shoulder girdle have been pressed together, 

 causing the two plates to overlap each other 

 to the extent of about i cm . In addition to 

 reaching inward to the middle line, the 

 coracoid is extended so far backward that 

 its posterior edge is nearly on a line with 

 the posterior end of the interclavicle. 

 There is a prominent articular face on the 

 coracoid, opposed to the face on the scapula 

 and arranged to permit the same sort of an 

 oblique articulation with the head of the 

 humerus as occurs in the Pelycosauria. 



Between the two articular faces originates a deep elongate pit which 

 runs about 2 cm towards the precoracoid. It occupies much the same 

 position as the cavity between the scapula and precoracoid figured 

 in Pareiasaurus by Seeley and called by Furbringer the Incisura 

 {Fenestra ?) coraco-scapularis, but it does not open through the bone. 

 I cannot imagine the meaning of this pit, unless it is a scar formed 

 on the bottom of the humeral cotylus by the attachment of a very 

 strong ligament, such as sometimes occurs in the acetabulum. The 

 coracoid foramen cannot be made out. In the Pelycosauria it opens 

 at the base of the scapular portion of the humeral face, but I cannot 

 find it there in this specimen. However, it was undoubtedly present. 



The inward and posterior extension of the coracoids and pre- 



FlG. 9. — Rear view of 

 jaw shown in Figs. 7 and 

 8. Natural size. 



