NERVOUS SYSTEM. VERTEBRATA. 215 



known as the " natiform eminence," and as a result of this 

 prominence there is a deep vallecula Sylvii separating the 

 latter from the anterior part of the pyriform lobe and the 

 olfactory tubercle. 



In profile the brain presents a general resemblance to the 

 Feline type, although there are many differences. The 

 cerebral hemispheres of the Sloth are, in comparison with 

 those of the Cat, much more highly macrosmatic ; or, to 

 express the same fact more accurately, the neopallium is 

 relatively smaller in the Sloth. 



The anterior and posterior rhinal fissures meet in an 

 upwardly-directed arc, and the resultant conjoint fissure is 

 placed wholly upon the lateral aspect of the hemisphere 

 and on a much higher plane than the corresponding fissure 

 in the Cat's brain. 



A distinctive " Sylvian fissure " of the Feline type springs 

 from the apex of the rhinal arch and ascends with a slight 

 backward inclination for a short distance (fig. 87, j,). 



There is a deep sulcus (/9) which clearly corresponds to 

 the presylvian (or orbital) sulcus of the Carnivora. It 

 pursues a horizontal course across the blunt cephalic pole 

 of the hemisphere. Its mesial extremity (fig. 89, ft) is pro- 

 longed on to the inner face ; this mesial prolongation may 

 possibly represent a rostral sulcus. Its lateral extremity 

 does not quite reach the rhinal fissure in this specimen 

 (fig. 87, /3), but in some cases it joins the rhinal fissure and 

 presents relations to the latter and to the Sylvian fissure not 

 unlike the arrangement found in the brain of GaleopitJiecus. 



There can be little doubt as to the homology of the 

 arcuate sulcus S (figs. 87 & 88) with the combined supra- 

 sylvian and postsylvian sulci of the Carnivora. The 

 anterior limb of this suprasylvian arc (so we may call it) is 

 very short. There is a short horizontal branch from the 

 posterior part of the arc such as is often found in an analo- 

 gous situation in the Carnivore's brain. 



There is a very small diagonal sulcus (compare the Cat's 

 brain) in front of and slightly below the suprasylvian arc. 



There is a sagittally-directed sulcus (7) analogous to that 

 called " lateral " in the Carnivora ; it pursues a course 



