368 
On the Sesamoids of the Knee-Joint 
clearly distinguished between lateral fabella and cyamella, remarks* that in 
animals in which the ossiculum in gastrocnemius externus articulates on the head 
of the fibula, popliteus springs from the knee-capsule and from the capitidum 
fibulae not from the femur itself We have indeed lost the distinction between 
the two sesamoids although we shall sometimes continue to speak of the cyamella 
as the single large sesamoid of the Edentates, because it is peculiarly associated 
with the popliteus -f. The transition stage of the lemuroids in which fabella and 
cyamella were coming into close contact now provides much suggestiveness, which 
will be again emphasised when we come to the Marsupials. 
In Plate XXIII, Fig. 55 a the reader will find a photograph of Tamandua tetra- 
dactyla\ with the cyamella attached to the popliteal tendon originating in the 
popliteal groove on the lateral face of the external condyle. It will be easy to see 
how a not too careful articulator can mount this sesamoid on the surface of the 
external condyle. The cyamella itself articulates on the lateral side with external 
articular surface of the tibial head. This head projects over and downwards on the 
head of the fibula, which does not articulate with the femur. The large cyamella 
bears some trace of being a possible compound, i.e. cyamella and fabella. We 
have found this cyamella — without fabella — in : 
Bradypus tridactylus (two mounted specimens), Bradypus arctopithecius, Cho- 
loepiis hofmaimi, Gholoepus didactylus (two specimens where the cyamella appears 
to be almost in the position of an anterior lunula), Myrmecophaya tamandua, 
Manis dahnanni and Manis javanica. 
There is, we think, no doubt that in Manis we are dealing with a cyamella and 
not a lateral fabella. Owen, however, speaks of this sesamoid in Manis as an 
external fabella (loc. cit. p. 409). Windle and Parsons in their paper "Myology 
of the Edentates"! remark under gastrocnemius : "It is interesting to notice that 
all observers have recorded the absence of fabellae except in the Orycteropidae " 
(p. 1004). This statement seems to overlook Owen and Gruber's statements as to 
Manis, and Macalister's with regard to Tamandua and MyrniecopJiaga didactyla. 
In his paper 1 1 on the " Myology of Bradypus tridactylus " Macalister writes of 
the heads of gastrocnemius, and says that there are no sesamoids in the origins of 
the muscle as there are in Tamandua and Myrmecophaga didactyla. He then 
continues that Meckel refers to the Ai as possessing one of these in its origin and 
in the Megatherium one of these appears to have existed for the outer head of the 
gastrocnemius. Later referring to popliteus Macalister states correctly that the 
* Loc. cit. p. 65, (15). 
f It would be better to speak of it as the parafibula, except that in certain cases it has changed its 
position so as to articulate with the tibia. 
J Macalister in his " Myology of Bradypus tridactylus" {Annals of Natural History, 1869, p. IS) 
speaks of the large sesamoid in the tendon of popliteus and states that it does not seem to occur in 
Tamandua (!). 
§ Proc. Zool. Soc. London, 1S99, Tp. 990. _ , 
II Annals of Natural History, 1869, p. 15. . - . - . 
