58 PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
Pelvic Girdle and Posterior Limb. 
The pelvic girdle consists of a nearly square ventral plate, the 
pubo-ischium, corresponding to the pubes and ischia of higher forms, 
although here these parts are not differentiated. From this spring 
laterally two slender processes, the ilia, articulating with the distal 
ends of the sacral ribs and thus attaching the girdle firmly to the 
axial skeleton. The anterior portion of the pubo-ischium is wholly 
cartilaginous, having three small anterior projections, one median 
and the others lateral, but no ypsiloid cartilage is found. I was 
unable to find obturator foramina. On the middle of the lateral 
border is the acetabulum which is nearly surrounded by a thickened 
cartilaginous rim. 
The posterior two thirds of the pubo-ischium contain a pair of 
large centers of ossification, the cartilage persisting as a narrow 
median strip only. In the mid-ventral region, extending through¬ 
out its length, is a ridge for the attachment of muscles, the crista 
muscularis. 
From the outer border of the acetabulum springs the ilium, extend¬ 
ing antero-dorsally. The ventral part of the ilium is a flattened, 
bony shaft, constricted slightly at its dorsal end where it is contigu¬ 
ous with a small cartilaginous epiphysis, with the inner surface of 
which the sacral rib articulates. 
The pubo-ischium is slightly concave on its dorsal surface, thus 
making more room for some of the viscera. 
Th % femur is the longest bone in the body, and, like the humerus, 
is longer in proportion to the size of the animal than the femora of 
allied forms. It is much like the humerus in shape, having a rounded 
cartilaginous proximal epiphysis which articulates with the acetabu¬ 
lum, a long, cylindrical, bony shaft less flattened proximally than 
that of the humerus, and a slightly rounded distal epiphysis which 
articulates internally with the proximal end of the fibula and exter¬ 
nally with the proximal end of the tibia. 
There is a ventral ridge or trochanter on the proximal end of the 
femur and on the outer surface is a small lateral ridge, both being 
used for the attachment of muscles. The trochanter seems to corre¬ 
spond in position to the lesser trochanter of higher forms, but may 
not be morphologically the same. 
