THE SKULL. 



15 



THE CRANIUM. 



Although the skull in Triceratops and the allied genera is larger than that of any other 

 known land animal, living or extinct, the cranium proper, or brain case, is not unusually large, 

 while the brain itself is remarkably small as compared with the size of the animal as a whole or 

 of the skull alone. Only the bones of the occipital and parietal segments take any considerable 

 part in the formation of the brain case proper, and some of these are excluded. The post- 

 frontals do, however, in some cases form a very small part of the anterior portion of the 

 superior wall of that part of the brain case inclosing the olfactory lobe. The different bones of 

 the cranium proper were the first in the skull of the Ceratopsia to become coossified with one 

 another. It thus happens that the anatomy of this region of the skull is somewhat difficult to 

 interpret in adult specimens. Fortunately there are in the Yale Museum collections skulls of 

 a number of young individuals in which the sutures are still sufficiently distinct to show most 

 of the characters of the different bones of this region. One of the skulls (No. 1821), which 



J 



Fig. 5. — Skull of Triceratops prorsus (type), No. 1822, Yale Museum, as seen from left side. About one-sixteenth natural size. After Marsh. 



was made the type of Triceratops (SterrhoIopTius) flabellatus by Professor Marsh, is especially 

 valuable in this respect, being essentially a disarticulated skull. Unless otherwise stated in 

 the text, the following description of the skull of Triceratops will be based on this specimen. 



THE OCCIPITAL SEGMENT. 



All the bones of the occipital segment are present, though the supraoccipital is somewhat 

 reduced in size. 



In fig. 6 there is shown an oblique posterior view of these bones, with the parietals and 

 squamosals in position as seen from beneath the latter elements. 



The basioccipitals coossify early with the exoccipitals and leave no indication of the 

 sutures even in the skulls of comparatively young individuals. This is the case in the type of 

 T. flabeUatus. In the occipital condyle of a younger individual (No. 1831, Yale Museum) 

 forming the type of Torosaurus gladius, however, the sutures are still open and show that the 

 condyle was formed by the union of the basioccipital and exoccipitals. The basioccipital 

 constituted about one-third of the occipital condyle, but formed no part of the border of the 

 foramen magnum. The basioccipital is massive, and the processes are extremely heavy and 

 terminate in broad, rounded, rugose extremities, which have the appearance of articular sur- 



