1872.] 189 [Shaler. 
be maintained by the most vigorous selection. There is probably no 
point in the history of the mammalian series when this action is 
more required than in the passage from the lower mammalian to the 
human pelvis. Already in the anthropoid apes we find distinct 
marks of a change to accommodate the needs éf the heavy visceral 
mass so often thrown into a nearly vertical position. The outlet of 
the pelvis becomes more narrowed, and its sides turned in such fash- 
ion as to give a greater amount of support to the weight thrown upon 
it. In man this contraction goes still further; not only is the outlet 
made so small that the foetus escapes with difficulty, but the brain of 
the child is somewhat endangered by the reduced aperture and the 
compression it is subjected to. 
The conditions of the problem are more complex than would seem 
to be the case at first sight. ~The safety of the uterus leads to the 
smallest possible outlet through the pelvis, the preservation of the 
child tends to bring about the smallest possible skull. This is in turn 
met by the need of a large brain. This complication of needs seems 
to be met as nearly as is possible in the present state of the accom- 
modation. 
The need of support for the abdominal viscera may account for 
some other important modifications in the human body. ‘The change 
in the position of the sacral and caudal segments of the vertebral 
column may be explained on the supposition that it gives support to 
the soft parts which lie above it. While the trunk was horizontal 
the caudal seements could well be spared for the purposes they serve 
in the forms which have this attitude; when, however, the pressing 
needs of the vertical trunk demand all possible support, the modifi- 
cation of the caudal and sacral elements of the vertebral column 
for the purpose of giving this support, is quite a natural change. 
The axis of the pressure from the abdominal cavity through the pel- 
vic opening is so oblique that the sacrum opposes it at nearly right 
angles. It may be urged against this view that the sacrum is so 
formed in woman as to exercise a rather less effective resistance to 
the downward pressure than in man, though that sex is in greater 
need of the protection. This objection is quite met by the fact that 
the needs of parturition would necessarily admit a less reduction 
of this opening in woman than in man. 
The change in position and character of the sacrum and coccyx 
necessarily brings about a change in the position of the female organs 
of generation; this in turn alters the attitude in copulation. Inas- 
