290 DE. G. ELLIOT SMITH ON 



demonstration of this is givea Ijy Poucliet's figure of a cranial cast of Ori/cteropus*. 

 In a dorsal view of the actual brain the tuberculated lobtts 2}yi"iformis anticus is very 

 distinctly seen at the lateral border of the anterior part of the cerebral hemisphex*e 

 (fig. 3). 



In the specimen of OrycteTopus which we have so far been considering, the upper 

 boundary of the pyriform lobe is very definitely indicated in its whole extent by a deep 

 and clearly-cut rhinal fissure, Avhich begins anterioidy in the cleft between the apex 

 of the hemisphere and the olfactory peduncle, and proceeds backward in a direction Avhich 

 is practically horizontal (fig. 2). The posterior half of the fissure descrilies a very slight 

 arc whose convexity is directed ventrally. Upon being traced backward the rhinal 

 fissure extends on to the caudal surface of the hemisphere and proceeds transversely 

 inward, as vre may observe in a view of the ventral surface of the brain (fig. 1). The 

 fissure ultimately reaches tlie mesial surface of the hemisphere and then ceases abruptly 

 (fig. 4). In the -whole of its course the fissure lies about midway between the upper and 

 lower surfaces of the hemisjihere. 



The term ^ssitra rhhudis may be most conveniently employed to designate the whole 

 of this extensive fissure, as I have applied it in the above description, and not only to 

 the anterior part as Krueg uses it f . The anterior jmrt of the fissure, wdiich forms the 

 upper boundary of the lohus 'pyrxjormis anticus, may be distinguished as the fissura 

 rhinalis anterior, and for the posterior part of the fissure we may adopt Krueg's name 

 "Jissura rhinalis jiosterior." The term "rhinal fissure" may be used to apply to the 

 combination of these two fissures. The dee}) cleft between the olfactory peduncle and 

 the apex of the hemisphere is sometimes regarded as part of the rhinal fissure. If we 

 admit this, the rhinal fissure begins and ends on the mesial surface of the hemisphere in 

 Oryctero2n(>s (fig. 4). 



In the brain Avhich I have hitherto been describing, the features of the extensive 

 undivided rhinal fissure were clearly defined in its whole extent, and presented an 

 exactly similar appearance in both hemispheres. But both of the brains in the Museum 

 of the lloyal College of Surgeons present a peculiarity in the disposition of the rhinal 

 fissure, in which, while they agree the one with the other in both hemispheres, both diff"er 

 from the type specimen Avhich we have been so far considering. This peculiarity consists 

 of a separation of the anterior from the posterior rhinal fissure. The anterior rhinal 

 fissure begins anteriorly in the ordinary manner, and forms the upper boundary of the 

 anterior jiyriform lobe in the whole of its extent, but then ceases without joining the 

 l^osterior rhinal fissure. The posterior rhinal fissure extends forward above the anterior 

 rhinal and pursues a course for some distance parallel to the anterior fissu.re. Thus the 

 cortex of the pyriform lobe is connected to the cortical area lying above the rhinal 

 fissure, now generally known as imllium, by a narrow process of cortex lying between 

 the overlapping extremities of the two parts of the rhinal fissure. This condition has 

 been somewhat schematically represented in fig. 5. 



* G. Poucbet, op. cii., ' Journal de TAnatomie,' &c. torn. vi. pt. t. fig. 3. 



t Julius Krueg, " L'eber die Furchen auf der Grosshirnrinde dor zonojjlaccntak'ii SiiugetLiere," Zeitschr. f. 

 wissensch. Zoologie, Bd. xxxiii. ISSU, p. 610. 



