NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 37 



olfactory bulbs and their roots or peduncles, and particularly more 

 slender across the pyriform lobes. It may, however, have been a 

 little less elongate in the cerebral portion than in Hyracotherium, as 

 the latter was figured by Edinger (1948, fig. 2). It seems, however, 

 to have reached a rather similar stage of development. 



The olfactory bulbs as seen in the rubber mold are distinctly less 

 divergent than in the Phenacodus cast and dorsoventrally less com- 

 pressed. There is a longitudinal fissure separating the lobes on the 

 dorsal surface, but which seems much less deeply impressed than on 

 the ventral surface. Moreover, on the ventral surface this fissure is 

 much less wide open and does not extend posteriorly dividing the 

 olfactory peduncles as it does in Phenacodus. In Meniscotherium 

 the ventral surface of the olfactory roots shows a gentle concavity, 

 which changes to a gentle convexity posteriorward, and a slight 

 longitudinal ridge on the mold — the trace of the suture between the 

 orbitosphenoids — extends posteriorward from near the fissure between 

 the olfactory bulbs to the optic chiasma. In the Phenacodus cast 

 the deep fissure extends almost to the chiasma. 



The neopallium in Meniscotherium is moderately elongate and 



Explanation of figures 2-4 



A., Ridge representing groove, possibly the cavernous sinus, and may have 



contained nerves III, IV, V 1 _ 2 and VI. 

 C, Cerebellum. 

 CE., Cribiform plate. 

 FL., Flocculus. 



f.Inf., Position of infraorbital foramen, 

 f.l.p., Filling of foramen lacerum posterius. 

 FR., Rhinal fissure. 

 Fr., Remnant of frontal bone. 

 M., General position or covering of midbrain. 

 ME., Mesethmoid. 

 MO., Medulla oblongata. 

 N., Remnants of inferior crests of nasals. 

 Np., Neopallium. 

 OB., Olfactory bulb. 

 OR., Olfactory root. 

 PL., Pyriform lobe. 

 Pp., Paleopallium. 

 S., Sagittal or longitudinal sinus. 

 SI., Lateral sinus. 

 Tu., Impressions of turbinals. 



VII., Position of facial nerve in internal auditory meatus. 

 VIII., Position of auditory nerve in internal auditory meatus. 

 XII., Filling of hypoglossal or condylar foramen. 



