370 
On the Sesamoids of (he Knee- Joint 
cyamella and not a fabella with which we are concerned*. The maximum con- 
fusion seems to be introduced by Macalister's paper of 1875 f. Writing of popliteus 
in Chlamydophorus he says : " I found no sesamoid bone in its tendon, as it lies 
under the external lateral ligament, nor does Hyrtl mention the existence of one. 
In the three-toed Sloth there is a large sesamoid bone. It is similar in Choloepus. 
There is no sesamoid bone in the Orycteropus, but there is in Gyclothurus and 
Rholidotus. There does not appear to be one in Myrniecupliaga or in Tamandua" 
(p. 266). The latter statement is incorrect. The statements as to Bradypus and 
Choloepus are correct, but Macalister adds Chlamydophorus to Oi'ycteropus as with- 
out cyamella. 
Turning to gastrocnemius\ he says that Chlamydophorus^ has the usual two 
heads neither of which possesses a sesamoid. There are no sesamoids in Bradypus, 
but Meckel found one in his specimen [we have already seen that Meckel found a 
popliteal not a gastrocnemic sesamoid]. No sesamoids exist in Choloepus didactylus. 
In Orycteropus there is a sesamoid bone in the outer head. [Humphry says he found 
a sesamoid in both heads !] A similar one exists in Cyclothurus and Tamandua. 
[This last statement is incorrect with regard to Tamandua, it may be correct but we 
have found only the cyamella in three limbs of Cyclothurus. If it were correct Cyclo- 
thurus would be the one Edentate that has both cyamella and lateral /a6eZ^a.] As 
Chlamydophorus has neither fahellae nor cyamella, it must be classed with Dasypus 
sexcinctus rather than with Orycteropus. 
Putting aside Humphry's statement with regard to Orycteropus which may have 
referred to an anomalous specimen, we have no case in which both fahellae occur 
in the Edentates. Even if Macalister's statement as to Cyclothurus be correct, we 
have only one case in which both cyamella and lateral fabella are present, and only 
two cases in which lateral fabellae have been recorded at all. There are two cases, 
Dasypus and Chlamydophorus, in which neither /«6e^/oe nor cyamella appear. 
Unfortunately we have been able to examine relatively few moist knee-joints 
of the Edentates, and have had to trust largely to other investigators and mounted 
specimens. This is especially undesirable in the case of lunulae. We know, however, 
that they certainly exist in the Edentates, for example in Megatherium cuvieri, and 
in Bradypus sexcinctus, which have anterior lunulae, and in Prodontes gigas which 
has a mesial posterior lunula. We also think it safe to say that the specimen of 
Orycteropus examined by us (there were alas ! no sesamoids m situ) had purely 
cartilaginous semi-lunars, i.e. no lunulae. 
* The mounted specimen of Orycteropus capensis in the Museum of the Royal College of Surgeons 
has what seems to us a cyamella or parafibular sesamoid, but it is mounted on top of the external 
condyle! In the mounted specimen of Manis aurita the cyamella or parafibular sesamoid rests in what 
we think a much more natural position, i.e. between lateral condyle and head of fibula. It has been 
slightly separated from the latter for the sake of photography : see our Plate XXV, Fig. 67. 
t "Anatomy of GhJamydopliorus truncattis with Notes on the structure of other species of Edentata," 
Trans. Royal Irish Academy, Vol. xxv. p. '219. 
+ Loc. cit. p. 267. 
§ We have examined two specimens of Chlamydophorus and find no fabellae or cyamella. The tibia 
and fibula are distally fused, and the latter is the more important member. 
