marsh.] TRICEEATOPS. 213 



THE SCAPULAR ARCH AXD FORE LIMBS. 



The scapula is massive, especially below. The shaft is long and nar- 

 row, with a thin edge in front and a thick posterior margin above the 

 glenoid fossa. The distal portion has a median external ridge and a 

 thick end (PI. LXTI, fig. 1, sc). 



The coracoid is rather small, and in old individuals may become 

 united to the scapula. It is subrhombic in outline, and is perforated 

 by a large and well-defined foramen. Xo indications of a sternum have 

 yet been found in this group. 



The humerus is large and robust and similar in form to that of 

 Stegosaurus. In one individual it is nearly as long as the femur, prov- 

 ing that the animal walked on all four feet. The radius and ulna are 

 comparatively short and stout, and the latter has a very large olecra- 

 non process, as shown in PI. LXVI, fig. 3. 



There were five well-developed digits in the manus. The metacar- 

 pals are short and stout, with rugose extremities. The distal phalanges 

 are broad and hoof-like, showing that the fore feet were distinctly 

 ungulate (PI. LXIX). 



THE PELVIS. 



The pelvis in this group is very characteristic, and the three bones, 

 ilium, ischium, and pubis, all take a prominent part in forming the 

 acetabulum. The relative size and position of these are shown in PI. 

 LXVII, fig. 1, which represents the pelvic elements as nearly in the 

 same plane as their form will allow, while retaining essentially their 

 relative position in life. 



The ilium is much elongated, and differs widely from that in any of 

 the known groups of the Diuosauria. The portion in front of the ace- 

 tabulum forms a broad, horizontal plate, which is continued backward 

 over the acetabulum, and narrowed in the elongated, posterior exten- 

 sion. Seen from above, the ilium, as a whole, appears as a nearly hor- 

 izontal, sigmoid plate. From the outside, as shown in the figure, the 

 edge of this broad plate is seen. 



The protuberance for the support of the pubis is comparatively 

 small and elongated. The face for the ischium is much larger, and 

 but little produced. The acetabular face of the ilium is quite narrow. 



The pubis is massive, much compressed transversely, with its distal 

 end widely expanded, as shown in the figures (PI. LXVII). There is 

 no true postpubis, but only a small postpubic process. The pubis 

 itself projects forward, outward, and downward. Its union with the 

 ilium is not a strong one, and is similar to that seen in the pubis of 

 Stegosaurus. 



The ischium is smaller than the pubis, but more elongate. Its shaft is 

 much curved downward and inward, and in this respect it resembles 

 somewhat the corresponding part of the pubis of the ostrich. There 

 is no indication that the two ischia met closely at their distal ends, 

 and they were probably united only by cartilage. 



