Karl Pearson and Adelaide G. Davin 
377 
suggest that the " Knotenpunkt " nature of the hxteral fabella is a phenomenon to 
be accounted for. We must seek for an important structure to which these muscles 
could have been originall}' attached, and which in a pre-vestigial stage had a use 
value*. The supernumerary head oi popliteus arising in the fnhelln, connects the 
lateral fahella at once with the ciiainella in the principal head of jjopliteus as 
possible parts of the same original structure. The next point is to consider what 
changes have taken place in the attachment of popliteas. There is no doubt that 
in the course of evolution popliteus has migrated from the head of the fibula to the 
lateral face of the external condyle. Take the cyamdla with the popliteal tendon 
attached still both to the condyle and to this sesamoid and place it at the head of 
the fibula; place the lateral fahella on top of the ci/amella; fuse them together 
and we have by no means a bad representation of the muscular attachments of the 
highly flexed marsupial knee-joint and their relations to the parafibular sesamoid. 
Fuse this parafibula to the head of the fibula and we have a rough representation 
of the muscles of the knee-joint of the Monofcremes. 
Let us examine first the Monotremes. Popliteus in Echidna arises frotn the 
extremity of the process at the top of fibula instead of from the external condyle. 
Gastrocnemius is a slender and delicate muscle arising from the internal condyle; this 
is really the internal head, and the external head appears to be replaced by Salens 
which "arises by tendinous fibres from the posterior and outer margin of the 
singular process at the summit of the fibula." This is Mivart's account^ of these 
muscles ; he does not refer to plantaris. 
Manners-Smith has dealt with Ornithorhynclinsl , and describes the knee-joint 
musculature as follows: 
He tells us that gastrocnemius is a large muscle arising by two distinct heads, 
a larger from the fibular crest and a smaller from " the lower end of the femur." 
It does not fuse with the salens. The femoral head, he states, is supplied by the 
external popliteal. Soleus arises from the fibular crest and from the shaft of the 
fibula. A few fibres only arise from the tibia. Manners-Smith contradicts Owen's 
assertion that a large proportion of the fibres arise from the tibia and asserts that 
it is certainly a mistake. He gives no information about popliteus or plantaris. 
Our drawing (Plate XX, Fig. 42) shows the external head of gastrocnemius having 
no attachment to the external condyle and the internal head attached to the 
internal condyle. 
In Reptiles popliteus arises from the fibula§, probably also from a groove on the 
external condyle and when it exists from the parafibular sesamoid i|. According to 
* As we have previously remarked we cannot consider a structure which has only an occasional and 
anomalous occurrence to have real "use" value ; it can only be degenerating, i.e. vestigial. 
t "Anatomy of Echidna hi/stri.r,'' Tranit. Linnean Society, London, 1866, p. .394. 
J " Anatomy of Ornit)iorlii/nchus," Proc. Zoolocjical Society, London, 1894, p. 707. 
§ Mivart, "Myology of Iguana tuberc.vlata," Proc. Zoological Society, London. 1867, p. 796. Poplileu.t 
arises from tibial aspect of head of fibula. 
i| See our p. 389, and the drawings of Varunus, Plate XXIV, Figs. 64 a and 64 h. 
