274

244

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. LXIX. 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 inter condylar 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 mammilar eminence (t) ; a smaller 'intercondylar'
tubercle (i) 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 1, 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 (o)
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 (m),
commencing from near the base of the procnemial process, and terminating on the inner
side of the extensor-tendinal canal, above the bridge (l) ; 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. The canal (f) of the
extensor tendon is crossed by a broad bridge of bone (l), is medial in position, not
toward the inner side, as in Dinornis 2 ; its lower outlet is transversely oval, and imme-
diately above the intercondular 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 (shown in fig. 5), which is not so developed in dinornis.

As compared with the tibia of Aptornis, the most striking differences in that of
Cnemiornis are seen in the development of the ectocnemial and more especially of the

1 The lower head of the 'gastrocnemius internus' rises from this part of the tibia in Apteryx (p. 59,
pl. XIV. R**) 2. Pl. XXV. fig. 4 f.