246 PROFESSOR OWEN ON THE GENUS DINORNIS. 



A reference to the subjoined table of admeasurements will show that t 4 (PI. XXV. 

 & XXVI. fig. 3.) is thicker in proportion to its length, has relatively broader proximal 

 and distal extremities, and a longer ridge for the attachment of the fibula. 



Tibii 



The anterior ridge c at the proximal end of the bone is nearer the middle in t 4 than 

 in t 2 (PI. XXV. & XXVI. fig. 1.), the interspace between that and the external ridge 

 being of the same breadth in both, notwithstanding the difference of total breadth. 

 The external proximal ridge curves more abruptly outwards from the shaft of the bone 

 in the small than in the large tibia, whereas the contrary character ought to have been 

 manifested if the difference of size had depended on difference of age, such muscular 

 ridges being more strongly produced in old than in young birds. The shaft of the bone 

 is flatter antero-posteriorly, compared with its breadth, in the small than in the large 

 tibia, and is more nearly triedral, owing to the greater flatness of the inner and anterior 

 surface and the less rounding off of the inner margin. All the four tibiae of from fifteen 

 to sixteen inches in length correspond in these differential characters, when compared 

 with either of the two gigantic tibiae ; and the two mutilated shafts of the smaller tibiae 

 equally differ in the subtriedral character from the mutilated shaft of the large tibiae. 



At the distal end of the bone, the angle formed by the posterior contour of the con- 

 dyles is of a diflerent form in t 2 (PI. XXV. fig. 2.) and t 4 (PI. XXV. fig. 4.) : in the 

 latter the outer condyle forms a greater proportional share of the articular surface, and 

 the line of the inner one g extends more abruptly backwards. 



All the shorter tibias, as before observed, present the characters of full maturity ; the 

 ridge for the fibula and those at the proximal end of the bone are quite as strongly de- 

 veloped as in the tibiae of double the length. 



In the tibia of a half-grown Ostrich I find the antero-external ridge, which in the 

 adult projects strongly from the head of the bone, in the state of cartilage, the fibular 

 ridge undeveloped, and both articular extremities in a state of epiphysis and incom- 

 pletely ossified : the same conditions which influence, as has been already remarked, 

 the tardy ossification in the Ostrich must have been still more operative in the Dinornis, 

 in which the absence of air in the femur indicates as low a development of the respira- 

 tory system as in the Apteryx. 



If this reasoning be admitted to establish the maturity of the bones < 3, < 4, < 8, < 9, 

 it equally proves that of the tibia t 11 (Pi. XXV. & XXVI. fig. 5.), which bears the 



' According to the obvious jiroportions of the articular extremities when entire. 



