186 ROYAL NORTON CHAPMAN 
the sacral vertebrae he termed the sacral axis (fig. 3, Sa.). A 
line passing through the junctions of the ischium and the pubis 
on both sides of the obturator foramen designates the obturator 
axis (Os). Another line, drawn along the ilum through the 
middle of the sacral articulation and the center of the acetabu- 
lum bears the designation of the iliac axis (Ja). The iliopectin- 
eal axis ([/p) is determined by a line traversing the union of 
the ilium with the pubis in front and with the ischium behind. 
This author concludes that in the phylogeny of the Mammalia 
the iliac axis (Ja) has tended to form a more acute angle with 
the sacral axis (Sa), that the angle formed between the iliopectin- 
eal axis (//p) and the sacral axis (Sa) has approached a right 
angle, and that the angle between the obturator axis (Oa) and 
the sacral axis has become more and more acute. ‘That is, the 
pelvis, which in the Reptilia (fig. 1) was nearly perpendicular to 
the vertebral column, has approached a horizontal position. 
The symphysis is said to move posteriorly, until it is formed 
largely by the ischial bones rather than the pubic bones. 
G. E. Dobson (82) incidentally included descriptions of the 
estate of the pelvis in his study of the Insectivora. The nature 
of the symphysis pubis in the families treated is mentioned, but 
no generalizations are given. 
W. Lecke (’84, ’92) considered the pelvis and the rectus 
abdominis muscles of the Insectivora from both the vhylo- 
genetic and ontogenetic points of view. His conclusions will be 
referred to later in this paper. 
H. L. Osborn (94) concluded that the symphysis proper of 
the pocket gophers (Geomys bursarius) was absent and stated 
his belief that the bone present in the male, forming a ‘pseudo- 
symphysis,’ was an ossification of a tendon and not a part of 
the pubic (or ischial) bone. 
Broek (14) and others have made studies of the pelvis of 
man and the apes in which correlations with the habits of loco- 
motion have been found and described. There is a vast amount 
of literature dealing with the human pelvis but, since it does 
not bear directly upon the subject at hand, it has not been in- 
cluded in this discussion. 
