ENDOCRANIAL NATURAL CASTS 



263 



Moodie (1922) described a small Merycoidodon cast which he provisionally referred to 

 M. gracilis. It was 60 mm. long; the cerebrum was 36 mm. long and had a maximum width of 

 32 mm. It had a volume of 20 cc. of water. This compares in every way with the cast of M. cul- 

 bertsonii, except that the cerebrum had no complexities, a feature which might have been due to 

 adolescence. A larger cast, apparently of a more mature individual, also showed no complexities in 

 the sulci of the cerebrum. The length of the latter, including the olfactory lobe, is 48 mm. and the 

 maximum width 35 mm. Moodie wrote that "The outer ends of the olfactory bulbs are flattened 

 obliquely against the ala ossis frontalis, thus causing the bulbs to end in median sharp points. The 

 upper surfaces of the bulbs are smooth and rounded with a cleft 4 mm. wide and 6 mm. long separat- 

 ing the anterior parts. They join the cerebrum by a common base." 



Some of these casts show unequal development on the two sides in both species. This character, 

 as well as the others noted above, are shown in a dozen or more well preserved endocranial casts 

 of Merycoidodon in the Marsh Collection at Yale. 



Fig. 186.— Eforeodon socialis Marsh. Endocranial cast. Cat. No. 1 3 1 18a Y.P.M. Nat. size. (After Thorpe, 1931.) 



Eforeodon: Marsh (1884, fig. 73) reproduced a dorsal view of the endocranial cast of 

 Eforeodon socialis, shown in position with the skull outlined around it. He gave no description, 

 either at that time or subsequently. This brain cast, Cat. No. 131 18a Y.P.M., was found at Scotts 

 Bluff, Nebraska, in 1874, with the cotype skeletons of Eforeodon socialis. 



The cast (Fig. 1 86; PI. L, figs. 1-2) is about the size of that of M. culbertsonii, and its nearest 

 general correspondence is with that of Sus, among living forms. The general relations show that 

 the relatively large olfactory bulbs were well in advance of the cerebrum, so that the anterior (trans- 

 verse) portion of the anterior sulcus rhinalis is wide and deep. The bulbus oljactorius is oval-shaped 

 and curves upward in advance of the frontal pole of the hemisphere. The bulbs are separated 

 through about one half of their vertical diameter by the fissura longitudinalis cerebri. The olfactory 

 bulbs of Sus are also large, and in both brains the tuberculum olfactorium is prominent. 



The cerebrum is medium-sized and rather low, its crest being just in advance of the transverse 

 fissure. The superior surface slopes gradually forward, not after the abrupt manner of the slope in 

 the horse, but more like that of the pig. When viewed from above, the shape of this portion is 

 that of an apically truncated pyramid, whose base is near the transverse fissure, that is, the maximum 

 transverse diameter is not just posterior to the middle, as is usual in many recent ungulates, but is 

 nearly at the posterior extremity. The two hemispheres are separated by a thin median ridge, the 

 sagittal sinus, which forks posteriorly and terminates in the deep, well-marked fissura transversa 

 cerebri, separating the cerebrum and cerebellum. The deep lateral sulcus extends longitudinally 

 along the posterior half of the dorsal surface. Its direction is forward and upward, whereas in the 

 pig and horse it runs backward and upward. The deep suprasylvian sulcus is convexly curved in 

 lateral view and bends posteriorly downward toward the posterior rhinal fissure. The ramus 



