292 DK. G. ELLIOT SMITH ON 



The I'liinal fissure thus forms a very clear boundary in the whole extent of the lateral 

 and caudal extremities of the hemisiohere between the pyriform lobe and the histo- 

 logically and morphologically distinct area of pallium. But ujjon the mesial surface of 

 the hemisphere (fig. 4) the upper margin of the pyriform lobe blends with the pallium 

 without any clear external indication of the line of junction. In this part of the 

 liemisphere the jiyriforra lobe extends around the postero-inferior angle, and is partly 

 limited in front by the loAver joart of an arcuate cleft — the ^/issar a hippocampi. But 

 below the hippocampal fissure the pyriform lobe seems to be continuous with a peculiar 

 oval body, which, for reasons to be subsequently explained, will be distinguished as the 

 " tuherculuni hippocampi " or " hippocampal tubercle." The height to which the lobiis 

 pyriformis extends upon the mesial surface is indicated by the indentatiou \\\)o\\. the 

 posterior margin of the hemisphere, which is the termination of the rhinal fissure (fig. 4). 



If Ave compare these basal regions of the cerebral hemisphei"e of Orycteropiis with 

 those of the Great Ant-eater, Ilyrmecophaga juhala, which in size and general mode of 

 life presents some resemblance to the African representative {Orycteropiis), we find a 

 general agreement bstween the two forms, but at the same time a number of interesting 

 points of diff"erencc. Although ihe figures and descriptions of Forbes * have added 

 much in clearness and exactness to the earlier observations of Gervais t, we still lack a 

 faithfid representation of these basal regions of the hemisphere of Myrmecophaga. 

 The bulhus olfactorius is relatively almost as large as that of Orycteropus, but it is not 

 so pointed, nor is it indented by any fissure such as we have seen in the latter. It is 

 also attached to the hemisphere by a large rounded peduncle, whose relations are 

 analogous in the two forms. The luherculum oJfactoriiim is not so elongated as it is in 

 the Aard-vark {Orycteropus), and presents a somewhat quadrilateral form. The tractus 

 olfactorius presents the same general features, but in Myrmecovhaga ends in a prominent 

 elliptical nodule, which is situated in the vallecula Sylvii immediately in front of the 

 emineutia natlformis and at the lateral margin of the locus perforatns (fig. 6). This 



Fig. 6. 



loc. perforst. 



nerv. II tnbercal.' ol/act, 

 tract, opt. ,■ ^ ,, . 



\ : . . tract, olfact. 



VJ, • y » -- Alob. prrifonn, 



rXmf^imlfmK /fsnoia dcntata 



f^^'^^ll/ Irl /""f- "'■Mill. 



m\Wk//////if """ °°"''" 



%vyJ^U-tpfJ gaogl. interped. 



Parh of tlie ventral surface of the brain of Myrmecojihaga juhata. Sligbtlj' reduced. 



little nodule, which has been indicated in the figures by the name tuherculum tractus 

 olfactorii, has been described in the Hedgehog {Erinaceus) by Ganser $, and is found in 



* Op. cii. Proc. Zool. Soc. London, 1882. t Op. cit., Nouvelles Archives, t. v. 



t S. Ganser, " Uebcr das Gcbiru des Mauhvurfs," ilorphologiscbes Jahrbuch, Ed. vii. 1882. 



