HATCHER: OSTEOLOGY OF HAPLOCANTHOSAURUS 25 
nearly flat surface. In the drawings this distortion has not been entirely elimi- 
nated. 
The ischiac peduncle is broad and sessile with the transverse diameter of the 
articular surface for the ischium considerably exceeding the anteroposterior 
diameter. 
The pubic peduncle is elongate, extending far below the inferior border of the 
ilium. It forms most of the anterior border of the acetabulum. The articular sur- 
face for the pubis has the transverse diameter greater than the anteroposterior. At 
its base the pubic peduncle is supported internally by the parapophyses of the dorso- 
sacral and the first true sacral vertebra as shown in Plate V., Fig. 11. 
The ilium is produced far in front of the pubic peduncle into a broad anterior 
blade. At its extremity this anterior blade of the ilium is broad instead of pointed 
as in Diplodocus and Brontosaurus. In superficial area the anterior blade of the 
ilium constitutes nearly one half of that element. Internally it is supported by the 
powerful and widely expanded diapophysis of the dorso-sacral. 
The ilia are not produced far behind the ischiac peduncles and the posterior 
blades are therefore short but rather broad. 
The upper one-half of the acetabular border is formed by the ilium, the pubic 
and ischiac peduncles and the acetabular bar formed by the united extremities of 
the parapophyses of the three true sacrals. 
The anterior extremities of the ilia of opposite sides are very widely separated 
and the posterior extremities less decidedly so while in the middle, both superiorly 
and inferiorly the ilia of opposite sides approach more nearly to each other. It thus 
happens that the diapophyses and parapophyses of the three true sacrals are shorter 
than those of the dorso-sacral and sacro-caudal. 
The Pubis (Plate IV., Fig. 3,and Plate V., Fig. 2).—The pubis is proportionately 
short and stout and greatly expanded proximally. At their distal extremities the 
internal borders of the pubes were in contact for a short distance only. Above this 
point of contact, when in position, the pubes were separated by an elongated aper- 
ture 500 millimeters in length, while above this aperture they meet again and form 
an elongated pubic symphysis about 300 millimeters in length. In either instance 
the union between the pubes of opposite sides was ligamentary. The direction and 
position of the superior of the two pubic symphysial surfaces is horizontal and ven- 
tral rather than vertical. The pubis forms the antero-inferior one fourth of the 
acetabulum. The pubic foramen is very large and somewhat elliptical in outline ; 
just posterior to and above it there is an extended sutural surface for contact with 
the ischium. 
