THE TRIAS OF GRAAFE EEIXET. S. AFRICA. 419 



OrnitliorJiynclius (PL XYI. fig. 8) and Ecliidna (fig. 9), and also, 

 though less marked, in certain Marsupials (Phascolomys * and Noto- 

 therium f). 



The length of the bone here described is 10| inches ; the breadth 

 of the proximal end is 5| inches ; that of the distal end is 5 J inches ; 

 that of the shaft across the deltoid (/, /) and tricipital (cZ) crests is 

 5| inches ; below these crests the breadth suddenly decreases to 2J 

 inches ; and the thickness (ancono-thenal diameter) of the shaft here, 

 including the bridge (Z?), is 2| inches. 



The head or proximal articulation (ct) is indicated by the greater 

 breadth of the convexity of that end of the bone towards the ento- 

 tuberosity (c), where it is 1^ inch ancono-thenally ; it is continued 

 of similar character, rough as for syndesmosal articulation, but losing 

 breadth, to the upper border of the ectotuberosity (h). The deltoid 

 crest (/), continued distad and ulnadfrom this tuberosity for an extent 

 of 6| inches, swells out into a rough surface at its end (/'), the 

 narrower distal border of which extends radiad at right angles to 

 the axis of the shaft and is continued into the bridge of bone (k) 

 which crosses and completes the entepicondylar canal (o, o). 



About halfway down the deltoid ridge a second lower one is con- 

 tinued from its thenal margin upon the thenal surface of the shaft 

 (at e, e), and represents the pectoral ridge. 



The border of the humerus, continued from the entotuberosity (c), 

 extends obliquely thenad, distad, and ulnad, subsiding upon the thenal 

 surface of the bone (c), and, with a similar thenal inclination of the 

 deltoid ridge (6, /), renders the proximal third of the intervening 

 thenal surface of the shaft {g) slightly concave transversely. Thia 

 surface, regaining its level, continues distad uninterruptedly to the 

 bridge (Z:). The thickened border or production of the humerus 

 from the entotuberosity (c) may be regarded as the teretial ridge. A 

 distinct process (c/), to which the term "tricipital" seems applicablej:, 

 extends, independently, from the radial border of the shaft midway 

 between the angle of the entotuberosity and that of the entepicon- 

 dyle (^). The extent of the base of this tricipital ridge or process 

 is 2| inches ; it projects | of an inch from the line or contour of the 

 radial border of the humeral shaft. 



Prom the least radio-ulnar diameter of the shaft below the del- 

 toid and tricipital crests, the bone rapidly expands to the breadth 

 above noted, which includes the ent- (^) and ect- Qi) epicondylar pro- 

 ductions. The short narrower part of the humeral shaft is crossed 

 obliquely by the " bridge " (Z;), the length of which may be put at 2 

 inches, its breadth at 8 lines. The length of the outlet (o') of the 

 entepicondylar canal is 1 inch 3 lines ; its breadth is 5 lines. The 

 distal joint-surface {I) for the antibrachium is developed from the 

 ulnar half of the expanded distal end of the bone; it is simply 

 convex, and projects mainly from the thenal surface of that end. 

 The ectepicondyle (7i) is continued proximad as a thick supinator 



* Researches on the Fossil Eemains of the Extinct Mammals of Australia (4to, 

 1877), p. 36], pi. ci. t lb. p. 517, pi. cxxvii. 



\ As affording origin to part o'" the triceps muscle in Monotremes. 



2p2 



