264 THE MERYCOIDODONTID^ 



lateralis suprasylvii is short and shallow, while the ansate sulcus is also short but deeper than the 

 former, and the deep coronal sulcus is prominent. The ramus descendens suprasylvii is discernible 

 but faint. The short presylvian sulcus is shallow. The deep sulcus rhinalis separates the pyriform 

 lobes and other ventral parts of the brain from the rest of the hemispheres. The inferolateral sinus 

 is shallow and widely open. Ridges, formed in the fossae of the median cerebral arteries, may be 

 discerned in advance of the pyriform lobes and below the rhinal fissure. 



The cerebellum is comparatively large and, with the medulla oblongata, rises slightly higher 

 than the crest of the cerebrum. It is separated from the cerebrum by a deep, wide transverse fissure, 

 which housed the tentorium cerebelli, and overlies the position of the pons. The greater diameter is 

 transverse. The posterosuperior part of the posteromedian lobule of the vermis cerebelli is missing, 

 but its crest probably was situated well aft, as in Merycoidodon. Instead of being curved in a semi- 

 circular form, as in the brains of nearly all recent ungulates, the dorsal outline of the vermis cere- 

 belli is oblong, gently curving anteriorly, and probably with an abruptly vertical posterior termina- 

 tion. The anterior lobe or lingula does not fill the interval between the cerebellar peduncles so 

 completely as in recent ungulates. The vermis maintains the same diameter, 9.5 mm., throughout 

 its length, thus differing from modern forms, in which it usually swells anteriorly to form nearly 

 all of the anterior part of the cerebellum. The two hemispheres are separated from the vermis by 

 the paramedian fissures. These hemispheres are nearly flat on their dorsal side, and in outline, as 

 seen from above, are right triangular, with the sides of the right angle abutting against the vermis 

 and the transverse fissure. 



The cerebellum of Sus is much more compressed in an anteroposterior direction than is that of 



Eporeodon. 



The medulla oblongata is dorsally concealed by the cerebellum. The shape in vertical section is 

 quadrilateral, has nearly the same vertical and transverse diameter, 15 mm. and 18.5 mm., and 

 seems to be somewhat compressed from above downward. 



The basilar part of the brain is nearly straight, the only important downward departure being 

 the ventral expansion of the pyriform lobe. In Sus this area is deeply indented from below, in the 

 region of the pituitary body and the roots of the optic nerves, to conform to the configuration of the 

 floor of the brain case. 



The restiform bodies are partially preserved and are very smooth. They diverge very close to 

 the cerebellum and form a triangular-shaped, very shallow depression, the posterior part of the 

 rhomboid fossa. The dorsolateral groove is fairly prominent. Apparently a portion of the tubercu- 

 lum cinereum is present, and its ventral surface is transversely convex. The fissura mediana 

 ventralis is only partially visible, its position being concealed except for the anterior part where it 

 terminates in a deep, well-marked pit, the foramen ccEcum. The very small corpus trapezoideum 

 is very faintly indicated. The pyramidal tracts are small, as in all ungulates. The roots of nerves 

 V, VII, and VIII are clearly indicated. 



The cerebral peduncles appear as two large rope-like stalks, which lead from the pons through 

 the foramen lacerum anterius with a slight anterior convergence. They represent the maxillary and 

 ophthalmic divisions of the trigeminus or nerve V. The rope or stalk-like appearance is due to 

 narrow longitudinal grooves in the skull, bearing the internal carotid arteries. The fossa interpe- 

 duncularis is plainly visible, because the pituitary body, which normally lies close to this fossa, is 

 missing. On the basis of the relative proportions of the whole brain and of the position which, in 

 life, the pituitary body would occupy, its size was probably about that of a small cherry stone. The 

 chiasma opticum is shown as a small downward projecting ridge located at the anterior boundary of 

 the interpeduncular fossa. This. ridge represents the convergence of the optic nerves. In advance 

 of the optic chiasma lies a deep longitudinal fossa, conforming to the basilar part of the brain case. 

 Laterally this fossa is bounded by the tuberculi olfactorii and the medial olfactory tracts. This 

 cast has a volume of 42 cc. of water. 



