PROFESSOR OWEN ON THE GENUS DINORNIS. 241 



principal generic character of the tarso-metatarsal bone in the Dinornis. The interspaces 

 of the three articular terminations are wider, the two lateral ones diverging more, and 

 being of larger size than usual ; they have also the median trochlear groove, but not so 

 deep as in the middle articular process. 



A section of one of the smaller metatarsals shows the confluent compact walls of the 

 three primitive constituents of the shaft, and the two tiiin bony partitions dividing the 

 cavity of the bone into the three separate medullary canals, as far down as the middle 

 of the shaft, where they cease, and a common medullary cavity is formed : the lower 

 part of the common medullary cavity is divided by a single septum into two canals, 

 which are continued into the coarse cellular structure of the divisions supporting the 

 articulations of the inner and middle toes, as in most other birds. 



The length of the tarso-metatarsal bone in the Dinornis is about half that of the tibia, 

 as will be afterwards more particularly demonstrated. In the tridactyle Emeu the tarso- 

 metatarsal bone is as long as the tibia ; in the Ostrich and the Bustard it is a little 

 shorter than the tibia. The still shorter proportion which it bears to the tibia in the 

 Apteryx of New Zealand forms a striking resemblance between this bird and the Dinor- 

 nis. But the Apteryx is distinguished from the larger Struthionidce not more by its 

 elongated slender bill than by the presence of a fourth small toe on the inner and back 

 part of the foot, articulated to a slightly raised rough surface of the tarso-metatarsal, 

 about a fourth of the length of that bone from its trifid distal end : the Dodo was also 

 tetradactyle, like the Apteryx. Thus the tarso-metatarsal bone of the Dinornis distin- 

 uishes that bird generically by its structure from the two last-named Struthionida, as 

 it does by its shorter and stouter proportions from the Cassowary, the Emeu and the 

 Rhea : the three well-developed anterior toes more obviously distinguish the Dinornis 

 from the didactyle Ostrich. 



Proceeding now to the comparison of the three most perfect tarso-metatarsal bones 

 of the Dinornis with each other, it will be obvious, from the subjoined table of admea- 

 surements, that they differ from each other in their proportions as well as in their size. 



Dimensions of the Tarso-metatarsals. 



ml. m 2. m .3. m 5. m 4. 



In. Lin. In. Lin. In. Lin. In. Lin. In. Lin. 



Length 18 6 14' 12 7 6 10 



Circumference 5 G 4 3 4 3 3 3 3 3 



Breadth of distal end 5 1 4 3 



Breadth of middle of shaft 1 1 1 1 G 1 C 1 5 1 3 



Thickness, or antero-posterior diameter of ditto .... IG 12 11 09 Oil 



Thus the circumference of the middle of the shaft is as 11 to 37, or less than one-third 

 in the longest bone (ml)'; in the second-sized entire bone (m 3)' it is a Uttle more than 



' According to the probable proportions of the articular extremities, when entire. 



« PI. xxvii. fig. 1. 'II'' %• ■-• 



& 



