PROFESSOR OWEN ON THE GENUS DINORNIS. 245 



two diverging lines of a denser cancellous structure, where the unclosed fissures exist in 

 the younger bone. The shaft of the bone m 6, which is less than half the length of the 

 mutilated one of the immature Dinornis giganfeus, equals it in breadth. 



nbice. (Plates XXV. and XXVI.) 



The chief generic characters of the tibia of the Dinornis are, the broad and wide con- 

 cavity (PI. XXVI. a) anterior to the proximal articular surface, the great breadth of the 

 ascending wall of bone, ib. b, for the implantation of the rotular or extensor tendon, 

 and, at the distal end, the slight anterior production of the lateral ridges of the trochlea. 

 All these characters are very strikingly distinctive when the tibia of the Dinornis is 

 compared with that of the Ostrich ; the difference is less, though well marked, in rela- 

 tion to the Emeu or Apteryx. The tibia of the Dinornis differs from that of all known 

 existing Struthious birds in the presence of the canal above the distal trochlea on the 

 anterior and inner side of the bone, formed by the oblique osseous bridge (PI. XXV. /) 

 across the extensor tendon. The affinity of the Dinornis to the Bustard and other 

 Grallce is indicated by this structure. The inner condyle or division of the distal 

 trochlea, ib. g, is relatively more produced backwards than in the Struthionida and 

 Grallts generally. 



The anterior crista (PI. XXV. c) at the head of the bone is less developed than usual. 

 The longitudinal ridge (PI. XXVI. d) for the fibula on the proximal half of the bone is 

 well marked ; but the fibula has not been anchylosed to it, nor is there any trace of that 

 bone in the present collection. The orifice of the medullary artery (PI. XXVI. e) is 

 close to the termination of the fibular ridge. 



Notwithstanding the great length of the largest tibiae, they are relatively thicker than 

 in the Ostrich and other known long-legged birds ; and this character of strength is 

 more marked in the smaller tibiae. Of the eleven more or less complete tibiae in the 

 present collection six are nearly of the same size ; four of these {t 3, t 4, t 8 and t 9, 

 PI. XXV. & XXVI. fig. 2.), which are entire and average a length of fifteen inches and 

 two-thirds, do not vary in length to the extent of one inch : the two shafts, t 5 and 1 10, 

 belonged to tibiae of the same dimensions. The three tibiae {t I, t 2, t 6), which are 

 double the dimensions of the foregoing, vary in length five inches, the shortest of the 

 three (PI. XXV. &XXVI. fig. 1.) being twenty-nine inches in length, the longest thirty- 

 five inches, and the one with incomplete extremities {t 6) obviously being of interme- 

 diate length. The length of the second long shaft {t 7) must have been nearly midway 

 between fifteen and thirty-four inches. The tibia (t II, PI. XXV. & XXVI. fig. 5.) is 

 not longer than that of the Great Bustard {Otis tarda). 



Both this and the tibiae t 3, t 4, t 8, t 9 have the characters of maturity as well 

 marked as in the two largest tibiae, but I shall at present limit the comparison between 

 i 2 and t 4, as the respective representatives of the gigantic bones, and of the four tibiae 

 which present half their dimensions. 



2 k2 



