31.6 DR. G. ELLIOT SMITH ON 



tlie shape and size of the brain in this family, they unfortunately convey a very imperfect 

 idea of the exact couJignration of the pallium of Chola'ims awdi Bradypas. This is all 

 the more unfortunate because the state of preservation of my specimens does not permit 

 me to describe the pallium with that amount of detail which is desirable. My observa- 

 tions liave been made mainly upon two representatives of each of tlie genera Bradyjms 

 and Cholcepus. 



In all the representatives of both genera to Avhich I "have had access, as well as nil 

 those to which reference is made in the memoirs quoted by me, there is a very well- 

 defined supraorl)ital sulcus (/3) presenting peculiar yet constant features. 



In Bradjipus iridaciylus the supraorbital sulcus (/3) appears to spring from the 

 anterior rhinal fissure near its middle, and proceed almost horizontally forward. At 

 its apparent origin from the rhinal fissure this sulcus is very shallou-, and may even 

 fail (fig. 11), but it rapidly deepens as it extends forward. It proceeds transversely 

 inward across the anterior pole of the hemisphere (fig. t^O), and deeply notches the 

 mesial surface of the hemisphere at its anterior border ( fig. 17 /3). 



Fiff. 20. 



Dor.sal surface of brain of Byai/i/pus triclacli/liif:. licduced to fy nat. size. 



In Cholcepus didactyhis, and apjoareutly also in Cholcppus Hoffmanni (judging from 

 Turner's figures), this sulcus presents a disposition exactly analogous to that I have 

 described in Bradypus (tigs. 12 & IS /3). 



In Bradydiis the sagittal sulcus (-y) is variable. In the specimen I have represented 

 (fig. 20) there is an extensive sagittal sulcus which is almost two thirds of the length 

 of the hemisphere. It crosses the posterior border to become continuous with the 

 sulcus a on the mesial surface. On the dorsal aspect of the anterior pole of the 

 hemisphere there is another sulcus which probably belongs to the same (7) series. It 

 begins just behind the sulcus /3, and extends backward for a short distance laterally to 

 the main part of the sulcus y. The representatives of the y series of sulci present a 

 slightly different arrangement on the smaller brain of Bradypus. On the left hemi- 

 sphere the fissure 7 is divided into two parts, just as we have noted in the first brain. 

 Of these the posterior, which is in continuity with the sulcus a', extends forward for 

 only about half the length of the hemisphere. The anterior fragment of the sulcus 



