44 
inférieure ; fait d’autant plus remarquable que cette machoire elle- 
méme est courte, et n’a d’étendue que dans la portion qui donne in- 
sertion aux muscles, c’est-a-dire sa portion postérieure et son aphyse 
coronoide.” e 
The peculiarities here pointed out in the cranium of those species 
which have a tail should not be regarded as characters necessarily 
associated with that appendage, but as incidental to the smaller spe- 
cies of the group; the tail also in this particular group being re- 
stricted to the smaller species. ‘The smaller species in any natural 
family of Mammalia,” says Professor Owen, “resemble the foetus 
of the larger species in the general proportional size of the brain and 
eyes.” This well-known law will, if followed out, explain pretty 
fully the nature of the differences in the crania of the larger and 
smaller Pteropi. The tail might probably have been either absent 
or present in both, without interfering with the results. Had M. 
Isid. Geoffroy instituted an examination of the cranium of one of the 
common species of Péeropi at several periods of its growth, he would 
at once have seen that previously to attaining the full size it had 
the cerebral cavity of manifestly greater relative capacity than after- 
wards ; and coincidently with this a greater thickness of the facial 
part is observable, but more especially a greater breadth between the 
orbits. My observations were first made from the examination of a 
series of skulls of Pteropus poliocephalus ; but I afterwards, to be 
quite satisfied that I was not noting a mere specific peculiarity, exa- 
mined those of P. edwardsii, P. edulis, P. rubricollis, P. hypome- 
lanus and P. dasymallus, and met with the same results. In the 
Pachysomes the same law also obtains, the skulls of the smaller 
species, such as P. duvaucellii which furnished M. Isid. Geoffroy 
with materials, having a relatively much greater cerebral region than 
those of the larger ones, such as P. stramineum and P. egyptiacum. 
These latter, although possessed of tails, do not differ at all materially 
in the general conformation of their crania from the true Pteropi. 
The same holds good with the crania of the Epomophori, but in a 
much greater degree. They vary from an exceedingly elongated 
form, as in EZ. macrocephalus, which has the facial part half its entire 
length, to a form which is remarkable for its shortness and convexity, 
and in which the facial part is scarcely more than one-fourth of its 
total length ; these skulls at the same time exhibiting no departure 
from the more important details of structure. For instance, all have 
the same shape and degree of development of the lower jaw, similar 
teeth, both in number and form, and similar modification of the 
form of the supra-orbital process of the frontal bone; but those 
species in which the facial portion of the cranium is long, are the 
larger ones; those in which it is short and thick, the smaller ones. 
Genus EpomorHorvs, Bennett, 1835. 
PacHuysoma, Temminck. 
General form of the body rather robust. The wings, ample in 
relation to the bulk of the body, are broad and rounded at the ends. 
