341' DR. »• ELLIOT SMITH ON 



From about the micl-poiut of the sulcus |S another sulcus takes origin, and after arching 

 mesially and caudally, extends directly backward as far as the posterior extremity of 

 the hemisphere. This sulcus is exactly analogous to the sac/lttal sulcus (y). In parts 

 this sulcus is very shallow and sometimes interrupted. In my specimen the sulcus is 

 more complete upon the left than upon the right hemisphere. 



The relations of the sulci /3 and y the one to the other are constant in the three 

 brains to which I had access. This arrangement differs but slightly from that obtaining 

 in Myrmecophaga, and which is generally prevalent among the quadrupedal Mammalia 

 having convoluted brains. The appearance of the combined sagittal and supra- 

 orbital sulci and the relation of the latter to the rhinal fissure present even greater 

 resemldance to the arrangement prevalent in the Ungulate brain than that of the 

 Carnivore. 



Midway between the sagittal sulcus and the rhinal fissure we find a series of frag- 

 mentary sulci whose extent is variable in different brains. The horizontal sulcus of Avhich 

 they constitute the rudiment is the homologue of that which Krueg calls the fissura 

 su-prasylvia in the Ungulata *. This sulcus is the homologue of the suprasylvian 

 sulcus of the Carnivora, and of the rudimentary representative (S) of this in 

 My rmecop h aga . 



In many Ungulata the "fissura suprasylvia " is horizontal, just as it is in Orycteropus, 

 but in others the more definite formation of a Sylvian fissure becomes associated with an 

 arcuate arrangement of the suprasyMan sulcus. In the Carnivora and Myrmecophagidce 

 the representatives of the suprasylvian sulcus always present a deep ventral concavity. 

 At the same time we must not lose sight of the fact that in many Ungulata the supra- 

 sylvian sulcus is decidedly arcuate. But we associate this arcuate condition of the 

 sulcus in question with a relatively much higher degree of pallial development than is 

 necessary to give rise to an arcuate condition in the Carnivora. In other words, an 

 arcuate suprasylvian sulcus is a characteristic feature of the Carnivore's brain, whereas in 

 that of the Ungulate it is an indication of a high state of pallial development. 



The fact that Ovycteropus jiossesses supraorbital (jS) and sagittal (y) sulci, which are 

 analogous to those I have already described in Myrmecophaga^ is not to be considered 

 as an indication of a close kinship, but merely signifies that both of these peculiar 

 animals belong to the great group of mammals which also includes all the Ungulate and 

 Unguiculate animals, as well as, in all probability, the Rodentia and Chiroptei-a. 



The fact that Orycteropus possesses a horizontal rhinal fissure, and consequently 

 exhil)its no tendency towards the formation of a pallial downgi'owth at the posterior part 

 of the hemisphere, distinguishes this peculiar mammal from the Ant-eaters and Unguicu- 

 lata, and suggests a rajjprochement with the Ungulata. 



But, it may be argued, the absence of a fossa Sylvii in Orycteropus clearly distinguishes 

 it from the Ungulata, in which a Sylvian fissure (in the same sense in Avhich this term 

 is used in speaking of the Carnivora) is well developed. But there are distinctions 

 between the Sylvian fissure of the Carnivore and the Ungulate. In the Ungulata it is 



* Julius Krueg, op. cit., Zeitsch. f. wissensch. Zool. Bd. xxxi. 



