312 F. B. Loomis — Osteology and Affinities 



parts as in modern camels. The deltoid ridge is well-marked, 

 rising jnst under the head and reaching down to about the 

 middle of the shaft. The supinator ridge is barely visible. 

 The trochlea stands at almost right angle to the length of the 

 shaft, is a little higher on its inner than on its outer margin, 

 and has the intertrochlear ridge but feebly developed and 

 situated near the middle of the ulnar side. The anconeal fossa 

 is low and deep, but does not perforate the shaft. 



The radius and ulna are completely fused throughout their 

 entire length, thus making a long, slender curved shaft. Using 

 the length of the humerus as a unit, the length of the ulnar- 

 radius would be 1*38, which is relatively longer than is the 

 case in Poebrotherium (1*15) or the modern camel (1'25), but 

 does not compare with the length of Oxydactylus. At both 

 the upper and lower ends of the radius occurs a groove indicat- 



Fig. 16. 



Fig. 16. Stenomylus hitchcocki, fused radius and ulna outer aspect, x 1/2. 



ing the original boundaries of the ulna, the lower end of the 

 groove penetrating so as to make a complete foramen. The 

 compressed olecranon process is moderately high and wide, the 

 upper anterior edge having in it a wide groove foi the extensor 

 tendon.* The humeral facets on the ulna are confined to the 

 superior border of the sigmoid notch and are not confluent 

 with the facets on the inferior border on either the inner or 

 outer side. To this statement I found in ten cases but one 

 exception, in which case the upper facet was confluent with 

 the lower along the inner side of the sigmoid notch. It is a 

 peculiarity of Poebrotherium and the Tylopoda generally that 

 the humeral facet on the upper border of the sigmoid notch is 

 confluent with the facets on the lower border only along the 

 inner side. This typical tylopod condition is characteristic of 

 the species S. gracilis^ and S. crassipes also. On the distal 

 end of the radius there are three facets for articulation with 

 the carpal bones, that for the scaphoid being the largest and 

 rectangular in outline ; that for the Innate being narrow and 



*This groove is characteristic of Poebrotherium and Oxydactylus but not 

 found in modern Tylopoda. Peterson does not find the groove in S. gracilis. 

 Ann. Carnegie Museum, vol. iv, p. 292. 



f Last cit. p. 455. 



