Karl Pearson and Adelaide Gr. Davin 
383 
as an extra lateral ligament in our case. We have already seen that the fusing* of 
the parafibular sesamoids is a possibility in the Marsupials, rare as it appears to be 
in the higher Mammalsf . It is possible that in certain individuals, or even in one 
or other species of opossum the cyaiuella may as a vestige be fused to the fibula, 
and so the popliteal tendon become an extra lateral ligament. 
Plaiitaris arises in Didelphys from the lateral femoral condyle j. 
It will be seen from the above that Didelphys, as far as the sesamoids of the 
knee-joint are concerned, is among the most advanced of the Marsupials. It stands 
at the opposite extreme to the Tasmanian Devil with its fused jjarafibula forming 
a fibular crest. The range marks the transfer of the gastrocnemius, popliteus and 
plantaris from fibula to femur and with them pass both lateral /rt6e//« and cyamella 
to the lateral femoral condyle. 
(19) Monotr ernes. 
We now come to the Monotremes and have to bear in mind the fundamental 
differences we have noted between the Oriiitliodelphia and the Monodelphia, in 
particular the existence of the parafibula, and the rearrangement of the muscular 
insertions of the posterior aspect of the knee-joint. We turn first to Ornitliorhyiichns 
(Platypus). Plate XX, Figs. 43 a and 43 h provide drawings of the femur and distal 
portions of tibia and fibula. The extraordinary development of the process at the 
distal end of the fibula will be at once noticed. From this fibular crest (see our 
Plate XX, Fig. 42) arises the lateral head of gastrocnemius, plantaris and popliteus. 
The patella is also attached to this expanded head of the fibula. This is vvell 
shown in the prepared specimen in the Mu.seum of the Royal College of Surgeons. 
The internal head of gastrocnemius is attached above the internal condyle of the 
femur. There are no fabellae^, no cyamella, and what is more remarkable no 
lunulae (i.e. because the latter are very conspicuous in the Reptiles). Thus platypus 
verifies what we have observed in the Marsupials : namely that, with the appear- 
ance of the fibular crest, there is associated a disappearance of lateral fabella and 
cyamella. Accordingly we see in the Monotremes the three muscular attachments 
which are associated with the lateral fabella in Man (see our Part I, p. 161) ; those 
of the external head of gastrocnemius, of popliteus and of plantaris, are now asso- 
ciated with the fibular crest. Manners-Smith tells us that|| soleus also arises from 
the expanded head of the fibula, but partly too from the shaft of the same bone. 
By the kindness of Sir Arthur Keith one of us was able to dissect the knee-joint 
of Echidna. There were no signs of any fabellae. The popliteal muscle followed 
* We must not be understood as suggesting that this "fusing" is something whicli may occur 
anomalously as in an adult individual ; it is specific in the case of the two parts of the parafibula, and 
vestigial when the parafibula is ankylosed with the fibula. 
t See our p. 373, first footnote. 
X This was so in our specimen, and Macalister says so also: see Anitala of Naturcd Histnri/, 
1870, p. 17. 
^ Meckel, loc. cit. pp. 634 — 635, had already noticed the absence of the fdhellae in Platypus 
(" Schnabelthier "). Gruber has not investigated the Monotremes. 
II "Anatomy of Ornithorhynchus," Proc. Zool. Soc. London, 1894, p. 707. He also notes the 
parafibular origin oi qastrocnemim e.rternus, but says nothing oi pojAiteus ov plantaris. 
