172 
On the Sesamoids of the Knee-Joint 
{h) Three hypotheses have been provided for the existence of the sesamoids of 
the knee-joint, namely : 
(i) The theory of their manufacture from cartilage by intensive stress or even 
by friction. Against this hypothesis it is adequate to cite the cartilaginous patella 
of the giant kangaroo, the persistent fabellae of the smaller primates, and the 
relatively rare occurrence in man, the persistent lunulae of the squirrel and the 
absence of lunulae except as anomalies in man ; the fact that the male has no 
higher percentage of fabellae than the female, and the general absence of fabellae 
in the greater and more massive anthropoids. 
(ii) The theory that the lateral fabella serves a useful purpose as strengthening 
the "Knotenpunkt " of a congeries of muscular attachments. Such a hypothesis of 
use value might be valid, if man were a living form developing for the first time a 
fiibella,. On the contrary more primitive types of the primates have it universally 
and the higher types appear to have lost it or at least to be losing it. If the 
lateral /(xfte/Za in man was there because it was of great service it would be difficult 
to explain why 7 need it and 93 7o get on very well without it ! 
(iii) The theory that the fabellae and the cyamellae are vestiges of some 
structure of earlier form, which has disappeared, and that hemisesamoids are not 
stages towards orthosesamoids, but the last steps in a degenerative process. Any 
such theory of the sesamoids of the knee-joint if valid will have to account for the 
marked differentiation in frequency, size and constitution of lateral and mesial 
sesamoids, and it will have to give some account of the structure of which they 
may be supposed to be the debris. It will also have to account for the muscular 
attachments of the sesamoids which we now find associated with the knee-joint 
in man. 
This third hypothesis seems to us the only reasonable one hitherto proposed for 
the existence of the sesamoids of the knee-joint, and we shall therefore endeavour to 
trace the evolutionary history of the fabella and cyamella. If we observe that in 
the earlier primate forms the sesamoids of the knee-joint are osseous, we can 
dismiss the question of hemisesamoids ; the only account we need give of them is 
that they are a measure of the extent of degeneracy, signposts to where an ortho- 
sesamoid once existed, and not the beginnings of sesamoids awaiting old age or 
intensive stress to make them osseous. We turn now to a study of the sesamoids 
of the knee-joint in living forms other than man, endeavouring to combine our 
own observations with those occasionally contradictory inter se of other observers. 
(To be continued) 
