Karl Pearson and Adelaide G. Davin 
157 
other words it is not the " always-present " nor " always-absent " categories that 
are the difficult ones, but the " sometimes present " category — needing statistical 
treatment — Avhich is the hardest to ascertain and yet is, perhaps, the most valuable 
for evolutionary suggestion. 
Wenzel Gruber starts by telling us (1875) that the fabellae in man have been 
known for 319 years, which gives us closely the date of the 1555 edition of 
Vesalius' work, and that those of the mammals have been known for 313 years, 
which is a close approximation to the date of Eustachius' work (permission to 
print 1562, issued 1564). There is no reference to Sylvius' commentary on Galen's 
De ossibu,^ (see our p. 144). Gruber at once sweeps away the statements that 
fabellae occur always in man, that they occur only or occur occasionally on the 
mesial side, that they are produced by stress or by friction, or that they occur 
most frequently in the aged or in males*. While an osteoma may and does occur 
in the head of both M. gastrocnemii it is far rarer than the true sesamoid and 
does not occur in the same situation. The origin of the fabellae is normal and 
perfectly analogous in the mammals and in man. Gruber then gives the statistics 
of his observations, to these we shall refer later ; they are rather obscurely 
expressed, Gruber not having a keen sense for figures. We shall refer here only 
to a few points which bear on his general conclusions. He says that for many 
years he examined the cadavers of human embryos in last month (total not stated), 
new-born children "in considerable number," "several" children aged one to seven 
and never in any of these nor in two five year old boys or in one seven year old girl 
did he find in the tendons of M. gastrocnemius, a cartilago hyalina, or fibro-cai^tilago. 
The wording does not strike one as referring to very copious material and possibly 
the material was inadequate for a negative conclusion. In 44 cadavers 10 to 17 
years Gruber found only the hyalina cartilago as hemisesaraoid ; in 426 cadavers 18 
to 83 years he found only ossified /aieWae, the orthosesamoids. In the external head 
he found only ossicula sesamoidea and hyaline cartilagines sesanioideae (our ortho- 
sesamoids and hemisesamoids), never fibro-cartilagiues or pathological ossifications 
(pseudosesamoidsf). In the internal head none of these occurred except a single 
pathological ossification, which he figures in Table III, Fig. 3^ (see our Plate IV, 
Fig. 8) and this would never be confused with a true fabella. From these data he 
concludes that (i) neither hemisesamoid nor orthosesamoid occur in the mesial head 
of M. gastrocnemius (p. 67), (ii) there is no trace of a sesamoid in the lateral head 
in the case of man before 10 years of age (p. 70), and (iii) orthosesamoids originate 
in a hyaline cartilago never a fibro-cartilago (p. 68). In other words our hemi- 
sesamoid according to Gruber is always hyaline and not fibro-cartilaginous. Here we 
think Gruber's lesser faults appear. He dogmatically asserts the non-appearance 
of hemisesamoid or orthosesamoid on the mesial side. He simply discards the 
* The existence of fabellae in man is wholly independent of age and occupation and does not arise 
from friction (p. 69). 
t Pathological ossifications in M. gastrocnemius are very rare in man and when they do occur are 
never in the neighbourhood of articular condylar surfaces, but in head of tendon close to femur and so 
removed far from site of fabella in man (p. 68). 
