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Show 1871.] 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 increased with the advancing age of the bird. Iu 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 Struthionidae, so in neither R. americana nor R. darwinii 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 fibulee could not be compared, as the bone was missing in the specimen 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 :- _?. americana. R. darwinii. Length of cranium from occipital condyle to top of upper mandible •. 5 9| 5 0 Length of ilium, measured along mesial line of dorsal surface of pelvis 11 0 8| 0 Length of sternum from proc. lat. ant. to posterior border 5 0 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 6g 5 3 . middle metacarpal 2 3 2 2 __ tftiaebrmisuao,r- mmeatastuarresdu sal ong inner surface 1171 1 053 1601 0 909 |