ENDOCRANIAL ANATOMY OF OREODON 293 



Brain stem and basis cranii. (Fig. 22.) The strand-like bulbo- 

 tubercular markings described in the other casts of the series- 

 are. evident in this specimen also. They are more clear on the 

 left side. The caudal expansions of the pyriform lobes are each 

 marked by longitudinal grooves. Between the prominences of 

 the olfactory tubercles and in front of the chiasma ridge is a 

 small elongated ridge of doubtful significance (vide infra). 



The pituitary eminence is well marked and the ridge corre- 

 sponding to the left internal carotid artery is equally prominent. 

 The fossa for the lodgement of the posterior clinoid processes is 

 deeper in this specimen than in any other of the series. The 

 basioccipital surface between the posterior lacerated foramina is 

 broader than in Specimen IV and two small pit-like depressions, 

 similar to those observed in the corresponding region in Specimen 

 II, are asymmetrically placed thereon. These depressions are 

 just caudad of the slight transverse pontine ridge. An indistinct 

 transverse irregularity of the basioccipital surface of the cast on 

 a level with the caudal margins of the internal auditory meati 

 may represent the caudal trapezoid boundary. 



Cerebral hemispheres. In most essentials the arrangement of 

 the cerebral sulci corresponds with that obtaining in Specimen 

 IV. In one particular, however, the sulcal pattern of this cast 

 presents a most significant variation and differs from that char- 

 acterizing all the other specimens. The peculiarity in question 

 is more evident on the left side and consists in the presence of 

 an elongated depressed neopallial area contiguous to the rhinal 

 fissure and limited dorsally by a long, slightly arched sulcus. 

 At its caudal end this sulcus cuts the rhinal fissure and rostrally 

 it is continuous with the presylvian sulcus. The cortical area 

 thus circumscribed is overhung above by two opercula bounded 

 respectively by the anterior and posterior ectosylvian sulci. The 

 latter sulci meet to form a well marked processus acuminis ecto- 

 sylvii. The disposition of limiting sulci about this depressed 

 neopallial area recalls in a striking fashion the condition obtain- 

 ing in Hydrochoerus capybara (Holl, 18, Taf. XVIII, fig. 1; 

 Elliot Smith, 1 1 , fig. 73) and reproduces in all essentials the rela- 

 tions characteristically present in this area in Moschus and 

 Cervus, and frequently present in Ovis and Capra. 



