38 



the ceratopsia: 



somewhat larger optic foramen {of, figs. 8, 31, and 32), by which the optic nerve leaves 

 the brain case, while above and a little anterior to this the two small foramina, marked ff 

 in fig. 32, enter the brain cavity. The pituitary fossa opens between and a little to the 

 rear of the sphenoidal fissures, as shown in fig. 31. It is deep and extends far back 

 beneath the floor of the median vesicle. The entrance is nearly circular and is constricted 

 just beneath its mouth. Near the anterior end of the pituitary lobe two small foramina 

 (pf, fig. 32) enter the pituitary fossa. The foramina for the carotid arteries enter the 

 pituitary fossa at its posterior extremity, as shown in fig. 32. The brain cavity is much 

 constricted just in advance of the optic foramina and this constriction becomes more 

 pronounced anteriorly, separating the cerebrum from the olfactory lobe, which is rather large 

 and much elongated as compared with the size of the brain as a whole. In the type of 

 Triceratops (Sterrholophus) flabellatus (No. 1821, Yale Museum) the olfactory nerves emerge 

 from a single median foramen, as shown in fig. 9 (see p. 18), while in the types of Triceratops 

 Jiorridus, fig. 27 (No. 1820, Yale Museum), and Triceratops prorsus (No. 1822, Yale Museum) 

 this foramen is divided into two by a median partition or septum. The brain cavity is entirely 



Fig. 33.— Longitudinal section of skull of Triceratops flabellatus Marsh, from No. 1821, Yale University Museum, showing the position and 

 extent of the brain cavity. One-sixteenth natural size. Modified by R. S. Lull from an unpublished drawing by Marsh, bo, Basioccipital; 

 d, dentary; exo, exoccipital; fr, frontal; h, supraorbital horn core; rax, maxillary; nas, nasal; nh; nasal horn core; no, nasal opening; pa, 

 parietal; pd, predentary; pf, post frontal; pi, palatine; pmx, premaxillary; q, quadrate; r, rostral; so, supraoeeipital; sg, squamosal; 

 x, sinuses beneath postfrontal bones; xo, postfrontal fontanelle. 



inclosed within the basioccipital and exoccipital and the basisphenoid and alisphenoid. The 

 expansion is greatest in the cerebral region and the cavity narrows posteriorly in the region 

 of the cerebellum. There is a marked constriction in the walls of the brain cavity immediately 

 above the internal opening of the foramen lacerum posterius, marking the union of the medulla 

 oblongata with the cerebellum, which is less perfectly separated from the cerebrum by a slight 

 constriction in the walls just in advance of the foramen ovale. The floor of the brain cavity 

 becomes much elevated just in front of the exit of the optic nerve, as is well shown in figs. 31 

 and 34, while the roof becomes lower and the lateral walls converge, resulting in that decided 

 anterior constriction which separates the olfactory lobe of the brain from the cerebrum. 



THE SENSE ORGANS. 



Considering the comparative size of the olfactory lobe and the foramen or foramina for 

 the exit of the olfactory nerves, one would judge that the sense of smell was well developed in 

 the Ceratopsia. In the same manner the large and cavernous orbital cavities, with their ante- 

 rior borders projected well beyond the external surface of the skull, are indicative of large and 



