No. 428.] THE ANATOMY OF A DOUBLE CALF. 605 
side. The sacral vertebræ are not only bent as described 
but there is a twist in them so that the centra come to face 
inwards, and instead of looking downward they look toward each 
other. Each sacrum articulates on its outer side with an os 
innominatum of the usual form, consisting of ilium ischium and 
pubis, meeting to participate in the formation of an acetabulum 
for the reception of the femur of the paired leg of its own side 
of the body. The pubic bones meet ventrally and forma normal 

Fic. 4. — Ventral aspect of the bones of the sacral region. 
symphysis pubis. The two sacra articulate internally with a 
peculiar bone, evidently composed of two incomplete ilia. This 
bone presents anteriorly two crests, each with the usual relation 
to the corresponding sacrum. In the center of this median 
bone there is a ridge which ends bluntly in front, and poste- 
riorly meets a broad, thin, and somewhat tapering bone by a 
distinct suture. At the junction of these two parts is situated 
a shallow but distinct articular surface; it is the acetabulum of 
the median hind leg. It is very evident that the anterior bone 
