262 THE MERYCOIDODONTIOE 



Thus the presence of a true lobulus petrosus in Oreodon is a feature apparently unique among modern 

 ungulates, while in other respects the formatio vermicularis is of a generalized ungulate type. 



The large and specialized cerebellum in Oreodon is in striking contrast with the small and relatively 

 simply arranged neopallium of this form and affords an excellent example of the apparent independence of 

 these organs during phylogeny. ... 



It would seem, however, that a highly elaborated mechanism for static, sthenic and tonic muscular con- 

 trol, built on lines essentially similar to the corresponding organ of modern mammals could hardly have been 

 evolved independently of the neopallial efferent projection center whose action it supplements. Obviously 

 the alternative suggestion is that the neopallial efferent projection center must have been laid down and func- 

 tionally active in these early mammals, a conclusion which accords well with the prominent development of 

 the gyri bordering the coronal sulcus. 



Black gives the average measurements of four specimens as follows: 



Maximum transverse cerebral diameter 46 mm. 



Maximum interpyriform diameter 45 



Maximum fronto-occipital diameter 45 



Maximum cerebral height 32 



Volume of cerebrum 36 cc. 



Volume of cerebellum and brain stem 14 



Edinger (1929) calls attention to the fact that the average skull of M. culbertsomi is at least 

 100 mm. shorter than that of Sus scrofa, and that the differences in the brain sizes, as emphasized by 

 Black, are not really so great when the differences in skull sizes are kept in mind. The Sus brain 

 dimensions, corresponding to those above, as given by Flatau and Jacobsohn (1 899), are as follows: 



Length of the base of the brain 90 mm. 



Maximum length of cerebral hemispheres 73 



Maximum height of cerebral hemispheres 40 



Maximum breadth of cerebral hemispheres 54 



In comparison with these figures, Edinger (loc. tit., p. 185) gives Black's measurements of one 

 specimen as follows: 



Maximum overall length 87 mm. 



Length to posterior border of cerebellum 82 



Maximum length of cerebrum 46 



Maximum width of cerebrum 46 



Maximum height of cerebrum 31 



Leidy (1869) described briefly an endocranial cast of this species, broken at the anterior of the 

 cerebrum, and called attention to the dorsoventral compression of the cerebrum and its simplicity, 

 only four convolutions being present. 



Moodie (1915) noted "the absence of all complexities on an especially small, apparently 

 young brain." A larger brain cast he said (1922, p. 365) had a cerebral length of 40 mm., a width 

 of 38 mm., and the width of the olfactory bulb was 5 mm. This cast displaced 41 cc. of water. _ He 

 said, further: "On the base the tuberculum olfactorium is rounded and well marked. The pituitary 

 elevation is evident as an elongated elevated mound between the large rounded ares pyriformes." 



Brain casts of M. gracilis were described first by Gratiolet ( 1 859), who said that the voluminous 

 cerebellum of these reminded him of a similar condition in the "pachyderms." His measurements 

 were: length, 66 mm.; width, 36.5 mm.; and length of cerebellum, 21 mm. Gervais (1872) 

 likened the cast of this brain to that of Ccenotherium but recognized that it had somewhat more con- 

 volutions than the latter. Bruce (1883) compared endocranial casts of different species of Mery- 

 coidodon, including M. gracilis, and found them all similar in development, but of a slight variance 

 in size, width, and development of the segments. 



