362 
On the Sesamoids of the Knee- Joint 
external tibial tuberosity) in both, but not in the chimpanzee (p. 307). On the 
other hand he states that he did find in a chimpanzee (p. 297) a mesial fabella — 
i.e. the inner tendon of head of gastrocnemius contained a sesamoid. This result is 
of considerable importance. The consensus of opinion is against the occurrence of 
any fahellae in the chimpanzee but the occasional anomalous appearance of a 
fabella, especially a mesial hemisesamoid, would be exactly what we might an- 
ticipate with the close relationship that exists between man and the chimpanzee. 
Hylohatinae. Hepburn in his memoir on " The Muscles and Nerves of the 
Anthropoid Apes" {Journal of Anatomy and Physivlogi/, 1892, p. 337), found 
a sesamoid bone developed in each tendon of origin ; in dealing with popliteus he 
makes no mention of the existence of a sesamoid, which he would have been 
pretty certain to have done had it existed. We dissected the knee-joint of a 
gibbon (Hylobates mvelleri) and found the mesial fabella only, no cyamella* and 
no lunulae : see Plate XXVII, Fig. 72. This result is in full accord with Sir Arthur 
Keith's expressed in his thesis: "Gibbon: sesamoids extremely variable even in 
adult animals. There may be one in each head or both may be absent or either may 
be absent" (p. 297). In Diagi'am 75 of Sir Arthur Keith's thesis figures the knee- 
joint of a gibbon, the internal head of gastrocnemius with large, the external head 
with minute sesamoid. He has never observed the cyamella in the gibbon. The 
existence of individual gibbons in which the mesial fabella only appears, while it 
may seem like the exception which proves the i-ule, is not so really, for the rule is 
that no species occurs in which the mesial fabella is invariably present and the 
lateral fabella invariably absent. The invariable presence of the lateral and in- 
variable absence of the mesial fabella is as we have seen characteristic of certain 
species f. 
The mounted skeletons of Anthropoidea, e.g. those at the British Museum 
(Natural History) and at the Royal College of Surgeons, are all "too clean" to 
show the sesamoids of the knee-joint. It may be hoped that in future the 
cyamella, where it occurs, will be preserved and mounted as well as the fabellae, 
both in these cases and those of the Old and New World Monkeys, although very 
often the fabellae are preserved in the latter. 
Simiadae (Old World Monkeys). We have already seen that the existence of 
both fabellae in the Old World Apes was known to Sylvius and Riolanus (see our 
pp. 144 — 145). Meckel gives a fairly extensive list of lemui'oids, New World and 
Old World Monkeys in which he had observed both fabellael- Gruber notes that 
he had found both in the genera Gercopithecus, Inuiis, Cynocephalus^, and Cebus 
* The tendon of popliteus was "horny," but there was no sesamoid. 
t It is worth noting that even in the gibbon Keith {'Thesis, p. 298) found the lateral fabella more 
frequently present than the mesial. 
t Loc. cit. S. 63i— 635. 
§ We have found both fabellae in 3Iacacus leoninus, M. pileatiis, MI. rhesus (several specimens), 
il/. iimus (Barbary ape), M. cijnomolgus (several specimens), Cyiiocephalus anubis, M. nemestriniis (two 
specimens), J)/, speciosus (Japanese ape), Cercopithecus lalandii (two specimens), Colobus ursinus, 
C. vellerosus, Nasalis larvatus (two specimens), Semnopithecus orientalis, S. entellus, Papio hamadryas, 
etc. etc. Burdach, Olg and others have noticed other cases from 1838 onwards. 
