56 



THE CERATOPSIA. 



THE PELVIS. 



As shown in fig. 60, the pelvis in the Ceratopsia is very characteristic. All three of the 

 elements usually found in the pelvis of the Dinosauria are present and enter into the construc- 

 tion of the acetabulum, which is more nearly closed internally than is common in that group. 



Fig. 60. 



-Pelvis of Triceratops ftabellatus Marsh, No. 1821, Yale Museum, as seen from left side. 



One-twelfth natural size. After Marsh. 



?7, Ilium; p, pubis; is, ischium; a, acetabulum. 



THE ILIUM. 



The ilium is the largest of the pelvic bones. It consists of a broad and elongate plate 

 much expanded anteriorly, but more pointed and somewhat thickened posteriorly. When 

 in position this iliac plate occupies a horizontal rather than a vertical or inclined plane, thus 

 differing materially from that position which this element assumes in other members of the 

 Dinosauria. Externally it presents throughout its entire length a rather thin and smooth 

 edge or border, but the internal border, save near the anterior extremity, is thick and presents 

 rugosities for contact with the transverse processes of the sacrum, as shown in fig. 5.5. The 

 anterior and posterior wings or blades of the ilium are nearly equal in length. Near the middle 

 the internal border of the ilium is greatly thickened and produced downward to form the supe- 



Fig. 61.— Inferior view of right ilium of Triceratops ftabellatus Marsh, No. 1821, Yale Museum, a, Anterior end; p, posterior; i, internal 

 border; e, external border; is, isehiac peduncle; pb, pubic peduncle. One-eighth natural size. 



rior border of the acetabulum and the isehiac and pubic peduncles. The isehiac peduncle is 



broader than the pubic, but not so much produced beneath the superior border of the ilium. 



In fig. 61 there is given an inferior view of the ilium of the type of Triceratops JlabeUatus 



Marsh, No. 1821, Yale Museum. This shows well the characteristic form of the ilium in the 



