116 MB. C. W. AKBEEWS ON EEMArNS OF ^PTOENIS [Feb. 6, 



In Siruthio the central cavity of the femur is large and smooth- 

 walled for about 6 cm. in the middle of the shaft, the cellular 

 bone being there absent. Above and below this it increases in 

 quantity, narro\\ing the cavity of the shaft and completely filling 

 the ends of the bone. As in ^pyomis there is a large pneumatic 

 foramen on the posterior surface about the level of the neck, and 

 also several smaller ones opening into the popliteal fossa. 



In the larger species of Dinornis the central cavity of the shaft 

 is small. This, however, is not owing to the development of 

 the bony reticulum, but to the great thickness of the walls, which 

 appear to consist of an outer hard compact layer and an inner 

 much thicker layer of soft bone, the innermost portion of which 

 alone is honeycombed so as to form the bony network. The 

 solid wall of the shaft of a femur 31 cm. long measures 2 cm. in 

 thickness. As in Apteryx there are no pneumatic foramina, and 

 the cavity of the bone must have been filled during life with 

 marrow. 



In the same collection there is another nearly complete femur 

 (figs. 1 & 2, 6), rather smaller than the one just described, and differing 

 from it so much that it will probably be found necessary to refer 

 it to a different genus. 

 Its measurements are : — 



cm. 



Approximate length 38-0 



Diameter of shaft from side to side at narrowest 



point 8-5 



Circumference at the same point 24*7 



Approximate width of distal end 16-5 



Circumference of neck 20-0 



It is therefoi-e evident that the proportions of this bone are 

 different from those of the femur referred to ^. titan. Thus, if 

 the length be taken as 100 in the two cases, then in the present 

 specimen the ^idth of the distal end will be approximately 43-4, 

 whUe in ^. titan it wiU be 51-2. Similarly, if the least circum- 

 ference of the shaft be taken as 100, then the proportionate width 

 of the distal ends wiU be 66-8 and 76-9 respectively.'? 



The chief points other than size in which this femur differs from 

 that referred above to JE. titan are : — 



(1) The trochanter is much less massive. 



(2) The head and neck, instead of projecting at right angles to 



the long axis of the bone, are turned somewhat upwards. 



(3) The middle of the shaft is roughly quadrate in section, owing 



to the flattening of the outer, inner, and posterior surfaces. 



(4) As was shown above, the distal extremity is proportionately 



less massive. 



(5) The popliteal fossa has a high outer border, formed by a 



rounded ridge running fron the outer condyle to the tuber- 

 ositv at the upper angle of the fossa. 



