Prof. Owen on Dicynodon tigriceps. 245 



straight, and moderately thick and rounded : the upper border, or ' crista,' soon 

 becomes thin on quitting the angle a, and is continued backwards and downwards, 

 with a slight degree of convexity, and at an acute angle with the anterior border. 

 The hinder or lower border is short, concave, and rapidly thickens as it approaches 

 the acetabular cavity. The outer surface of the ilium is slightly concave and 

 smooth : the anterior or antero-lateral surface is narrow, and divided by a broad ridge 

 of bone from the inner surface, which shows many longitudinal and slightly con- 

 verging grooves near the thin margin, indicative of the junction with the expanded 

 ribs of the first and second sacral vertebrae, which I suppose to have abutted against 

 or overlapped this part of the ilium. The posterior angle of the ilium (c) appears 

 to have projected backwards. The haemal element of the pelvic arch, consisting 

 seemingly of a confluent ischium {t) and pubis is), forms a strong and thick sub- 

 semicircular plate of bone, moderately concave externally, convex at its upper part 

 and upper inner part, slightly convex vertically and slightly concave transversely, 

 in the rest of the inner surface, which formed part of the wall of the pelvic canal. 

 Near the convexity, answering to what is termed the brim of the pelvis in Mam- 

 malia, is an eUiptical foramen, 1^ inch by 1 inch, in long and short diameters : it 

 is the commencement of a canal, which perforates the bone obliquely downwards 

 and forwards, opening externally below the thickened part of the pelvic brim, and 

 about two inches from the acetabulum, at o. The brim of the pelvis becomes 

 thinner as it approaches the symphysis pubis (s, s) ; and it has been more extended 

 apparently outwards, but has been here fractured. The symphysial surface is semi- 

 elliptic or reniform, 6^ inches in length, 3 inches across at its broadest part, forming 

 an acute angle with the outer surface, which it thus meets by a sharp border : the 

 lower part of the ischio-pubic bone is continued at an obtuse angle from the sym- 

 physial border, is at first thin, and then becomes thickened to form the projecting, 

 strong, roughened angle, answering to the ischial tuberosity (t). The space between 

 this process and the posterior superior spine of the ilium (c) forms a part answering 

 to the great ischiadic notch in Mammalia. Some traces of the original suture 

 between the ilium and the ischio-pubic plate are discernible in the articular cavity. 

 The following are the dimensions of the above-described os innominatum : — 



In. Lines. 



Total length, following the outer curve .... 21 



Length of the ilium 110 



Breadth of ditto at its base or labrum .... 90 



,, of the neck or narrow part 3 9 



Transverse diameter of acetabulum 5 



Length of ischio-pubis 80 



Breadth of ischio-pubis 9 



