2(56 THE MERYCOIDODONTIME 



ridge seems to have been separated by a thin bony plate which was not apparent in Eporeodon. The 

 eminence corresponding to the pituitary fossa is considerably larger than in the latter genus, and the 

 body itself must have been as large as a small cherry. The tuberculi olfactorii are large and 

 separated by a wide shallow fossa, unlike the narrow cleft in Eporeodon. Again, the depression 

 posterior to the pituitary eminence is shallow, wide, and flat, without the deep pit seen in the other 

 genus. This endocranial cast has a volume of 1 5 5 cc. of water. 



Measurements in millimeters 



Maximum length, exclusive of olfactory bulb 116 



Maximum length of cerebrum 67 



Maximum length of cerebellum 37 



Maximum width of cerebrum 65.6 



Maximum width of cerebellum 47 



Maximum distance between ventral edges of pyriform lobes 33 



Maximum vertical diameter of cerebrum with pyriform lobes 47.5 



Maximum vertical diameter of medulla oblongata and cerebellum 44 



Merycochosrus: This genus shows an endocranial cast (Figs. 187-188) sculptured after the 

 pattern of that in Merycoidodon, and the comparative sizes of cerebrum and cerebellum are the 



,-> 



Insula 



Mcdullo spinalis '. 



Medulla oblonqota 



Ostium ntaxillore 



Sinus maxilloris 



inferior 



', Sinus rooxillans inferior 

 [Pars anterior! 



Ostium occessonum 



Fig. 187. — Merycochcerus. Lateral view of endocranial cast and anterior sinuses. About 1/2 nat. size. 



(After Moodie, 1916.) 



same in both genera. Moodie (1916) compares the cast also with the brain of the sheep, to which 

 it is very similar. The cerebrum is 50 mm. long and 48 mm. wide, while the maximum length of 

 the entire brain, exclusive of the olfactory lobes, is 80 mm. The cast displaces 77 cc. of water. 



Cyclopidius: Cope (1884B, p. 504) stated that the cerebral hemispheres of this genus are not 

 large and barely rise above the level of the summit of the large cerebellum. The weakly defined 

 convolutions number three on each side. 



Conclusions and Summary: It now becomes evident that the brain of the various genera of 

 merycoidodonts, so far as known, did not advance to any appreciable extent, certainly not in the same 

 degree that it did in many of the contemporaneous groups. Naturally the size of the brain varied, 

 but the proportions remained nearly constant. 



While Eporeodon seems to have been a descendant from Merycoidodon, yet the evolutionary 

 change has been comparatively slight in general and is still less reflected in the structure of the 

 brain than in the skeleton. The arrangement of the sulci and gyri in Sus is more like that of 

 Eporeodon and much simpler than that of the brain of either the horse or the ox. 



