THE BRAIN IN THE EDENTATA. 317 



begins on the mesial side of the posterior fragment and extends forward towards the 

 sidcus /3, bitt just liefore its termination it gives off a peculiar hook-like lateral branch. 



On the riglit hemisphere the sulcus y is split up into three parts, of which the anterior 

 and posterior are very short and laterally placed. The intermediate segment, which 

 occupies about tlie middle two fourths of the hemisphere, overlaps both of the other 

 fragments on their mesial side. 



In the admiral)le representation of the dorsal aspect of a cranial cast of Brndypm 

 which Gervais gives, the sagittal sulcus is represented by a single and very definite 

 furrow which extends almost the whole length of the hemisphere. After comparing the 

 condition of tlie 7 series of furrows in Bradypus with the analogous sulci in Cholcppus, 

 it seems possible that the fragmentary sulci which we have found in the former may 

 represent the two sagittal sulci which we find in the Two-toed Sloth. 



In one of my specimens of Chola'pns didaclylm a sulcus begins near the lateral margin 

 of the posterior surface, and after pursuing a mesial course along the superior border 

 of the hemisphere it bends forward, at a distance of 7 mm. from the mesial plane, and 

 extends the whole length of the hemisphere till it meets the sulcus /3. At a distance 

 of 9 mm. from its cephalic limit this sulcus takes a sharp bend toward the mesial 

 plane and continues its course at a distance of about 4- mm. from the great inter- 

 hemispheral cleft. Erom the caudal extremity of the more raesially placed part of the 

 sulcus a much shallower sagittal sulcus arises and proceeds backward almost to the 

 posterior border of the hemisphere, dividing the area between the sagittal sulcus (y) and 

 the interhemispheral cltft into two equal areas. This condition is practically symmetrical 

 in the two liemispheres. 



In the second brain there were also two sagittal sulci, but tliey were apparently not 

 so complete (fig. 12) as those just described. 



In a figure which Pouchet gives of the dorsal aspect of the brain of a young 

 Two-toed Sloth two very complete and independent sagittal sulci are represented, of 

 which the lateral unquestionably represents the sulcus siKjiltalis of other forms. Again, 

 in the cranial cast of Cholcepiis which Gervais figures there are two very distinct sulci. 



In the brain of Choloepits Hnffmanni which Turner has figured, we find fragmentary, 

 sulci representing these two sulci. The proper sagittal sulcus crosses the posterior 

 margin of the hemisphere and bends to the lateral side of the mesial or subsidiary 

 sagittal sulcus, where it suddenly ceases. Further forward we find traces of the anterior 

 portion of this sulcus. 



The question as to the na' ure of the mesial sagittal sulcus naturally suggests itself. 

 It seemed at first not unlikely that this sulcus might represent the anterior part («") of 

 the splenial sulcus, taking into consideration the course of the a' element of the sjilenial 

 sulcus and the fact that it is not uncommon for this sulcus to extend on to the dorsal 

 aspect of the pallium in many Ungulates and other mammals. But the existence of a 

 very deep sulcus on the mesial surface in the usual position of a", and the extreme 

 shallowness of the mesial sagittal sulcus, lead me to discard this suggestion and to regard 

 the additional furrow as a mere mechanical product of the peculiar pallial growth of 

 Choloepus. 



