THE BEAIN IN THE EDEXTATA. 345 



ixmisnal to find the fossa Sylvii, or tlie fissui e wliicli is formed l)y the meeting of its lips, 

 so well defined in the neiohbourhood of the rliinal tissui-e as is customary in the Cariii- 

 vora. Sometimes, it is true, the posterior lip is as well defined as it is in Caruivora, as, 

 for instance, in the brain of the Pig (S/is) ; but very often the posterior lip, which we 

 have already noted as the most important boundary of the fossa Sylvii, is not so well 

 formed, and in mnny Ungulates tlie Sylvian fossa becomes reduced to insignificant 

 proportions. In some Ungulates it becomes so far reduced as to be a mere horizontal 

 depression ab:ve the caudal extremity of the anterior rhinal fissure, with no attempt at 

 the formation of a fissure. The most extreme instance of this reduction with which I 

 am acquainted is the Musk-Deer (Moschus moscJiiferns), excellent figures of which have 

 been provided for us l)y Tlower *. 



In this animal we find a brain of peculiar simplicity, which presents a remarkalde 

 resemblance to that of Orycteropus. If we compare Plovver's fig. 12 with the repre- 

 sentations of the lateral aspect of the hemisphere of Orycteropus (figs. 2 and especially 5), 

 this similarity will be at once apparent. In the two brains of Orycteropus in the 

 College of Surgeons we have already observed that the anterior is distinct from 

 the posterior rhinal fissure, and that the latter extends forward for some distance 

 above and parallel to the former. This arrangement becomes more intelligible when we 

 compare it with the condition in Moschus. In this interesting brain the posterior 

 rhinal fissure also appears to extend forvvavd above and parallel to the anterior rliinal 

 for a considerable distance. But the anterior rhinal fissure joins the posterior rhinal, 

 before the apparent anterior extension of the latter overlaps the former ; and in 

 addition the area between the two overlapping fissures is depressed, so tliat by com- 

 parison with Myrmecopliaya or any of the common Carnivores or Ungulates we find 

 in this depression the representative of the fossa Sylvii. In Orycteropus it is probable 

 that the apparent cephalic extension of the posterior rhinal fissure is intrapallial and 

 represents the upper boundary of the fossa Sylvii, the relation of which to tiic sulcus 

 j3 is identical with that which obtains in Ilyrmecophaga (tig. 7)- 



The configuration of the pallium in Orycteropus is analogous to that which is found in 

 the simplest form of Ungulate brain. The pallium in Orycteropus is relatively much 

 smaller than it is in Ilyrinecophaga, and this fact probably explains the great difference 

 in the size of the corpus caliosum in the two brains. It is also much smaller than 

 the pallium in any Ungulate with which I am acquainted. 



Tiedemann, Pouchet, and Turner, in the memoirs to which I have frequently 

 referred, have given figures and brief descrii^tions of the brain of the Two-toed Slotb, 

 and in Gervais's excellent figure of the cranial cast of Cholcepus the shape and size 

 of a brain of this genus are accurately represented. Leuret andPouchet have figured 

 the brain of the Three-toed Sloth, and Gervais has represented a cranial cast of this 

 genus. 



"While these contributions to our knowledge relieve me from the necessity of describing 



* W. H. Flower, ' Oii the Structure and Affinities of tlie 3Iisk-Deer,' Pi-oc. ZojI. Sao. London, March, 1875. 



