376 
On the Sesamoids of the Knee- Joint 
eome in contact with the femur on extreme flexure. This iigure throws much light 
on the position of the large lateral sesamoid in the Tasmanian Devil (see our 
Plate XXXIV, Figs. 89a and 896) and in Halmaturus (see our Plate XXXV, Fig. 90). 
In Pseiidochirm peregrinus, one of the phalangers, the lateral condyle of the 
femur articulates with the fibula and both lateral /a6e/^a and cyamella are present. 
The fibula was prolonged upwards and posteriorly into a wing on the top of which 
the lateral fabella was found. The cyamella is a small nodule or inner notch of 
fibula. The arrangement is somewhat similar to that of Didelphys. 
If the hypothesis developed in this paper be correct, namely that the lateral 
fabella and cyamella are vestiges of the break-up for the parafibula of an early 
mammalian evolutionary stage, we ought to find the lateral head of gastrocnemius, 
in whole or part, and the tendon of popliteus transferred to the capitulum fibulae. 
We shall turn shortly to the myology of the Marsupials and inquire whether there 
is any support for such a view. 
One of the noteworthy points of the Marsupials and Monotremes is the apparent 
absence of lunulae which are so definitely present in many reptilian forms. We 
have failed to find them in OrnithorJiynchus, or in the koala,, wombat and a variety 
of kangaroos. The alternatives before us are: to suppose that both Monotremes and 
Marsupials have lost original lunulae, although they occur regularly or at least 
as anomalies in many placentals, or to suppose both to have originated in a 
reptilian form possessing a fibular crest or a parafibula, but no lunulae. A similar 
problem arises in the case of the Ungulates ; we must suppose them to have com- 
pletely lost all sesamoids of the knee-joint, and so thoroughly that they do not 
even appear as in man as anomalies, or we must conceive them descended from an 
ultimate form which has never possessed parafibula or lunulae. 
(18) On clianges in the musGidar attachments of tlie knee-joint. 
If we look upon the lateral fabella and the cyamella in Man as vestiges of an 
earlier structure which has now disappeared, it becomes of importance to consider 
the evolutionary history of the muscles attached to these sesamoids. Does it 
indicate a ti'ansition of their attachments from one bone to a second which is 
compatible with a transfer of the sesamoids from one bone of the lower limb to a 
second ? W^e ventui'e to think it does, and shall endeavour to place before the 
reader in this section our reasons for believing that the transfer of muscular attach- 
ments fi'om the head of the fibula to the distal epiphysis of the femur has been 
accompanied by a transfer of the renmants of the parafibula to the lateral condyle 
of the femur. 
The muscles with which we are principally concerned are M. gastrocnemius 
(in particular the lateral branch), M. popliteus and M. plardaris. Gruber has gone 
so far as to assert that the lateral fabella serves a useful purpose as a " Knoten- 
punkt " directing on the posterior surface of the lateral condyle the movements of 
gastrocnemius externus, plantai^is, semimembranosus and occasionally M. popliteus 
biceps, when this anomalous supernumerary head of popliteus is present. Without 
accepting this interpretation of " usefulness " in a vestigial structure, we would 
