| OCR Text |
Show 116 MR. C. W. ANDREWS ON REMAINS OP MPYORNIS [Feb. 6, In Struthio 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, narrowing the cavity of the shaft and completely filling the ends of the bone. As in ASpyornis 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, b), 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 therefore evident that the proportions of this bone are different from those of the femur referred to AS. titan. Thus, if the length be taken as 100 in the two cases, then in the present specimen the wTidth of the distal end will be approximately 43-4, while in AS. titan it will be 51-2. Similarly, if the least circumference of the shaft be taken as 100, then the proportionate width of the distal ends will be 66-8 and 76-9 respectively.; The chief points other than size in which this femur differs from that referred above to AS. 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) A s 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 tuberosity at the upper angle of the fossa. |
