Karl Pearson and Adelaide G. Davin 
381 
ordinary fabella, it will be found to articulate with the articular surface of the 
lateral condyle. Turning to the muscular attachments Parsons states : 
The ffaafrocncnu'iis has the usual two heads, the outer of which has three oi'igius : (1) a small 
head from the outer side of the patella, (2) larger from the same place and separated from the last 
by the external ])oi)liteal nerve, (3) from tlie hirge fdhel/a over the external condyle and from the 
external semilunar cartilage. The inner head is normal in origin and has no fabella developed in 
it (p. 207). 
The so/i'i(s is absent unless the origin of the f/aKtrocnemiiin fi'om the scmi-lunai- i-artilage 
represents it. Meckel also de.scribes it as wanting. 
Plantaris comes from the external fubella*. 
Popliteus. arises from the external condyle, partly from in front of the gnjove, and partly from 
the groove itself, which is deep and narrow and not adapted for the tendon to lie int. The 
uuiscle also has an origin fi'om the external semi-lunar cartilage and fi'om the head of the fibula. 
We see in this typical description of a marsupial knee-joint, gastrocnemius, 
popliteus and plantaris all associated with the parafibular sesamoid. We see the 
muscles which largely arise from the fibular crest in the Monotremes now attached 
to the parafibular sesamoid, and the fragments of the parafibula will be carried 
with them as fabella and cyamella to their ultimate tendons of insertion on the 
lateral femoral condyle. We begin to see now why the early human anatomists 
associated the lateral fabella with numerous muscles, why popliteus (with its 
anomalous head) passes to fabella as well as to cyamella; how Gruber could confuse 
these two sesamoids, and why he emphasised so strongly the " Knotenpunkt " 
character of the lateral /«6e//rt. 
While llacropus seems to us to represent a later evolutionary stage of the 
parafibular sesamoid than Phascolomys, for in the Kangaroos we have various 
stages of disruption of the parafibula, while in the Wombat it may still be fused, 
the Phalangers form a more or less intermediate stage. They have a parafibular 
sesamoid of much the same form as the wombat's — quite different from that of 
the wallaby — and its form is seen to be clearly that of a fibular crest: see our 
Plate XXXIII, Fig. 8-5. 
As Cunningham has .shewn, gastrocnemivs in Phalaugista macnlata .springs from 
the posterior aspect of the fibula in its upper two-thirds, and plantaris from the 
parafibular sesamoid. Cunningham suggests that gastrocnemius is a compound 
muscle containing soleusl. The musculature is much the same as in the Koala 
{Phascolarctus cinereus), except that in the latter we did not identify plantaris^, 
which is also said not to exist in the Wombat. 
In Perameles nasuta we have the parafibular sesamoid, but the Pera.melidae 
are transitional to the Didelphyidae. Parsons has pointedii out that " the popliteus 
* That is the parafibular sesamoid. 
t Any marked popliteal sulcus has disap))earefl in MucrojJiis, see our drawing of the Wallaby, Plate 
XXXV, Fig. 90. 
J Challenger Report, Vol. v. p. 40. 
§ In the Koala there is a collatero-tibular ligament — the ultimate popliteal tendon connecting the 
parafibular sesamoid with the lateral condyle of the fenmr. 
II Journal of Aiiatonii/ and Physiology, Yo\. xxxiw Tp. 1900. 
