THE BRAIN IN THE EDENTATA. 319 



between these two brains is rendered all the more patent from the fact that the 

 crucial sulcus has almost disappeared from the brain of Genetta. In makin<j^ this 

 comparison with the Carnivora, it is interesting to note that in its developmental 

 history the pallium of Bradypus (judging from the data Poucbet has provided) closely 

 agrees wdth such carnivores as Fells. Krueg has shown that the arcuate suprasylvian 

 sulcns (S) makes its a2:)23earance very early in the Cat, and the illustrations of foetal 

 brains which Pouchet gives clearly show that the sulcus S is a deep and well-defined 

 i'urrow before any other furrow makes its appearance on the cranial aspect of the 

 pallium. The later appearance of the sagittal (y) and supraorbital (/3) sulci also agrees 

 in the two forms, and there is nothing (so far as I kaou) in the developmental history 

 to prevent the adoption of the view that the sulcus « of Bradypus is the homologue of the 

 Sylvian fissure of tiie iEluroidea. 



The sulcus S, which corresponds to the suprasylvian sulcus in brains possessing a 

 Sylvian fissure, presents some interesting points of difference in the two genera of Sloths. 

 We have already noted the constancy of this sulcus in Bradypus. It appears to be 

 equally constant in Cholappm, for all specimens — the two I have examined, those which 

 Pouchet and Turner represent, as well as the cranial casts — exhibit features which are in 

 agreement, while they all differ somewhat from the equally constant Bradypus type. 



In Cholcepus the sulcus S begins anteriorly (fig. 12) either from or in close proximity 

 to the anterior rliinal fissure, a short distance behind the sidcus /3. It then arches 

 upward, then backward parallel to the sulcus y, and finally bends do\Au\vard on the 

 posterior aspect of the hemisphere to terminate in the neighbourhood of the end oC the 

 rhinal fissure. In this manner an extensive arc is formed, wliieh is also well shown in 

 Pouchet's young Cholcepus didaotylus and Turner's Cholcepus Kojfmamii. 



The most puzzling feature of the brain of Cholcxpus is the absence of the sulcus ^i. In 

 none of the series of brains to wdiich I have had access is there any evidence of tlie 

 jjresence of this sulcus. This absence is the principal reason for hesitancy in proclnimin"- 

 the sulcus yi in Bradypus the homologue of the fissure of Sylvius in the Cai-nivore. For 

 if this sulcus is the fissure of Sylvius in the Three-toed Sloth, it is very strange that sucli 

 an important feature should vanish in the larger brain of the Two-toed Slotli, tlie 

 pallium of whicli is more complex. Between the arcuate sulcus S and the rhinal fissure 

 there is an additional horizontal or slightly arcuate sulcus which is lacking in Bradypus. 



In all the gigantic Ground-Sloths there is a very deep and extensive sulcus S forming 

 a huge arcuate suprasylvian sulcus, after the manner of the Carniv^ora. There seems 

 to be in addition a well-defined Sylvian fissure, or rather sulcus ih. There is therefore 

 in all the Sloths a striking analogy in the configuration of tlieir pallium to tliat of 

 the smaller Carnivores. 



In the smaller and more highly macrosmatic brains of the Armadillos w^e find a 

 much simpler pallium than among the other families. The series of variations in general 

 form and actual size which characterize the brain in the Dasypodidce are admirably shown 

 by the figures which Gervais has given of Cldamydophorus, Tatusia, Tolypeutes,Xenurus, 

 Basypus sexcinctus, Basypus villosus, and Priodon *. 



* P. Gervais, op. (it. pi. ii. figs. 0, 7, 8, 9, 11, 10, and 12 respectively. 

 SECOND SERIES. — ZOOLOGY, VOL. VII. i8 



