PROFESSOR OWEN ON THE GENUS CNEMIORNIS. 401 
outer condyle is less produced downward, and the rotular channel ( p) shallower and less 
defined. There is a rough depression above the fibular groove of the outer condyle 
in Aptornis, as in Dinornis. 
Tibia. 
The tibia (Pl. LXVI. figs. 1-5) is about the length of that of Dinornis geranoides, but, 
like the femur, is more slender in its proportions, and differs more widely in other 
particulars. ‘The chief of these is the much greater development of the ectocnemial (e) 
and especially of the procnemial (p) processes. The latter is a compressed, rhomboid 
plate, 1 inch 8 lines in vertical, 1 inch 3 lines in transverse or antero-posterior, extent ; 
it rises an inch and a quarter above the intercondylar tubercle (i), and is directed 
forward and a little outward. The ectocnemial process (e) is a thicker plate, of a trian- 
gular form, 1 inch 3 lines in the extent of its base, and the same in length ; it is divided 
above from the procnemial plate by a notch in the epicnemial common base (k) of 
the two lamelliform processes. The principal articular entocondylar surface of the 
proximal end (d) is applied to the broad back part of the inner femoral condyle: the 
ectocondylar surface is on a small mammillar eminence (t); a smaller ‘ intercondylar’ 
tubercle (z) projects into the intercondylar space of the femur. A small articular 
tract, on a prominence (s) on the outer side of the tibial head, articulates with the side 
of the head of the fibula. There is a strong gastrocnemial tubercle (g) on the inner 
side of the shaft, an inch below the produced margin of the entocondylar surface’, of 
which tubercle there is no trace in Dinornis. The fibular ridge (h, h) begins opposite 
the lower end of the gastrocnemial tubercle, and is 1] inch 7 lines in extent, rather thick 
and prominent, with the surface well defined; the canal for the medullary artery (0) 
begins about half an inch below this ridge, toward the back part of the bone. The fore 
part of the shaft (fig. 1) is traversed by a low and narrow intermuscular ridge, com- 
mencing from near the base of the procnemial process, and terminating on the inner 
side of the extensor-tendinal canal, above the bridge (J); a similar ridge runs along 
the outer border of the shaft from its middle to the ectocondylar fossa, near which it 
bounds outwardly a narrow, longitudinal, tendinal groove (n). The canal (f) of the 
extensor tendon is crossed by a broad bridge of bone (J), is medial in position, not 
toward the inner side, as in Dinornis® ; its lower outlet is transversely oval, and imme- 
diately above the intercondylar fossa (c) ; the anterior convexities of the two distal 
condyles are more nearly equal than in Dinornis: the trochlear canal (v) is less deep 
than in Dinornis. There is a well-marked tubercle near the middle of the entocondylar 
fossa (fig. 5, a), which is not so developed in Dinornis. 
As compared with the tibia of Aptornis, the most striking differences in that of 
1 The lower head of the ‘gastrocnemius internus’ rises from this part of the tibia in 4ptery« (Zool. Trens. 
vol. iii. p. 295, pl. 35. r**), 
* Zool. Trans. vol. iv. pl. 43. fig. 4 f. 
VOL. V.—PART V. 3G 
