364 



But the comparison with the bones of the young Ostrich brings to 

 light another character, which effectually decides the question of the 

 relation between the three different-sized bones of the Dinornis under 

 consideration. In all birds, the tarso-raetatarsal bone, as is well known, 

 is an aggregate of several distinct ossicles, the primitive separation of 

 which continues longest in those birds whose respiratory, circulating and 

 muscular energies are least developed. Thus in the Penguins the three 

 metatarsal bones are almost quite distinct from one another throughout 

 life ; and in the Ostrich and other Struthionida deprived of the power of 

 flight, the primitive separation of the metatarsals continues at their ex- 

 tremities to nearly full growth, as is exemplified in the tarso-metatarsal 

 bone of the young Ostrich, No. 1568. The tarso-metatarsal bone No. 

 1568, however, actually is what the present specimen, No. 1585, might 

 have been mistaken for, viz. a bone of a young individual of a gigantic 

 species of Dinornis, and the condition of this young bone demonstrates, 

 what could not indeed be reasonably doubted, that a more tardy ossifica- 

 tion coexists in the Dinornis, as in other Struthionida, with the absence 

 of the powers of flight ; which, therefore, as it establishes the maturity 

 of the tarso-metatarsal bone No. 1574, proves, a fortiori, that the smaller 

 tarso-metatarsal, No. 1585, with all the characters of mature age, could 

 not have belonged to a young: individual of either of the two larger 

 species. 



1586. A left metatarsal bone of the Dinornis didiformis, from which the pos- 

 terior parietes have been removed to expose the internal structure of the 

 bone. The line of union of the proximal or tarsal epiphysis is indicated 

 by the dense tissue by which it has been obliterated ; the coarse cancellous 

 texture of the proximal end of the confluent metatarsals soon subsides, 

 and a common medullary canal is exposed in the shaft of the composite 

 bone, partially divided by two thin septa into three equal compartments, 

 indicative of the three primitively distinct metatarsals : the medullary 

 cavity terminates below by dividing into brief continuations entering the 

 commencement of the divisions for the support of the three toes. 

 The dimensions of this bone correspond with those of the preceding. 



