18/1.] DR. R. O. CUNNINGHAM ON RHEA. 109 



the epicnemial process ; while in that of R. darwinii the process and 

 ridge are in a rudimentary condition, but would doubtless have in- 

 creased with the advancing age of the bird. In the latter an 

 epiphysis still remains ununited to the superior extremity of the 

 bone, while in the former it is firmly anchylosed and only indicated 

 by a roughened line. This epiphysis bears the epicnemial process, 

 aud also forms about half of the superior articulating surface of the 

 tibia. Very little difference is observable between the distal ends of 

 this bone in the two species. In neither is there any trace of suture 

 indicative of the junction of the tarsal element (astragalus), which 

 furnishes the trochlear surface, articulating with the tarso-metatarsal. 

 As in other Struthionidse, so in neither R. americana nor R. dar- 

 winii is there a bony bridge over the precondylar groove which 

 lodges the tendon of the extensor longus communis digitorum ; but in 

 both a tuberosity is present at the outer side of the groove. The 

 fibula could not be compared, as the bone was missing in the spe- 

 cimen of R. darwinii. Nearly all the differences exhibited by the 

 tarso-metatarsus of both species may probably be ascribed to the 

 difference in age. Thus this bone of R. darwinii differs from that 

 of R. americana in the complete separation of the tarsal element, as 

 well as that of the proximal extremeties of the three metatarsals. In 

 both skeletons the innermost of the three trochlear condyles of the 

 distal end of the bone is the shortest. In R. americana the tendinal 

 groove between the outer and middle trochlea is spanned by a bony 

 bridge, which is not fully developed in R. darwinii. The anterior 

 surface of the shaft of the metatarsus is more deeply hollowed out in 

 R. americana than in R. darwinii ; but in the latter the posterior 

 surface is more excavated than the former, and is further defined 

 externally by a strongly marked ridge. No noteworthy differences, 

 with the exception of those of size, appear to prevail between the 

 bones of the toes in the two species. They are proportionally 

 longer in R. darwinii than in R. americana. 



I subjoin a list of measurements of the bones : — 



E. americana. E. darwinii. 



Length of cranium from occipital condyle to m " in * • 



top of upper mandible 5 9| 5 



Length of ilium, measured along mesial 



line of dorsal surface of pelvis 11 8} 



Length of sternum from proc. lat. ant. to 



posterior border 5 3 10 



Length of coracoid 3 8 3 2 



scapula, measured in straight line 4 11 3 11 



humerus 9 3 7 9 



ulna 6 8 5 4 



radius 6 6| 5 3 



middle metacarpal 2 3 2 2 



femur 7 5 6 9 



tibia, measured along inner surface 11 3 10 9 



tarso-metatarsus II 10 



