402 PEOF. G. ELLIOT SMITH ON THE 



oln-iously the suprasylvian, orbital, and coronal sulci. In their subsequent developaaent 

 all of these sulci differ very cor.sidcrably from their homologaes in the Carnivora, so that it 

 is imjiortant to bear in mind that these sulci are regarded as homologous not only 

 because they are the most constant and similarly-placed farrows, but because their mode 

 of deA'elopment demonstrates their identity in the two Orders. 



Holl has recently demonstrated that the sulcus commonly called " Sylvian fissure " in 

 tlie Uucrulata is not homolos'ous with anv one of the various tvpes of pseudosvlvian sulcus 

 Found in the Carnivora. The " Carnivore jiseudosylvian " sulcus is sometimes found in 

 the Ungulata, e. g. in the genus Bos, but it is not that Avhich is commonly called 

 "Sylvian fissure." The latter (which we may call the "Ungulate pseudosylvian " 

 sulcus) is formed by the meeting of two sulci, \Ahicli are analogous to the ectosylviaa 

 sulci of the Carnivora *. 



After the sulci mentioned above, the most constant furrows are the lateral and diagonal 

 sulci. The former sulcus is not linked to the coronal sulcus as so often happens in the 

 Carnivora ; but it is sometimes joined to the suprasylvian sulcus. The diagonal sulcus 

 is much more constant than it is iu the Carnivora, and it is almost always placed just in 

 front of the anterior end of the suprasylvian sulcus. 



It is doubtful whether true homologues of the postsylvian and postlateral sulci are 

 ever found in the Ungulata. 



If we review the whole Ungulate Order so as to determine the constant sulci, 

 it will be found that those furrows only will be picked out Avliich, as the evidence of 

 embryology shows, represent those also found in the hypothetical primitive Carnivore. 



If we next examine the Edentata the same fundamental plan of sulci is again found. 



Thus in the genus Bradnpus we find pseudosylvian, suprasylvian, lateral, coronal, 

 orbital, and diagonal sulci arranged in a manner so like that seen in Fch's, that 

 one cannot question the homologies implied in the nomenclature just used. The 

 developmental notes publislied by Pouchet show that one is thoroughly justified in 

 maintaining this aIow. In the nearly allied, but larger, genus CIiolwpus the 

 pseudosylvian sulcus disappears ; it thus adds further testimony to the slight importance 

 of this sulcus. 



In the Anteater {Tamandua) there is always a definite orbital sulcus and a conjoint 

 corono-lateral, but it is a peculiar fact that in some cases the suprasylvian sulcus may be 

 absent, although in others it is well-developed. There is no pseudosylvian nor diagonal 

 sulcus. 



One of the most interesting and instructive brains in the whole mammalian series is 

 that oi IIijrmecoplKKjd Jalxda ; and all the more so because it is subject to peculiar 

 variations. 



The normal or common type of brain exhibits a conjoint corono-lateral, a postlateral, 

 a postsylvian, an orbital, and a jirorean sulcus, as in the Caruivora, and in addition a 

 ])seudosylviau sulcus of a peculiar nature. Moreover there are sometimes shallow 



*" Holl, " UebtT die IujcI dcs UDgulatcngcliirnfb,"" AvlIi. f. AiKit. u. Thys. 1000. Compare also Catalogue of the 

 lioyal College of Surgeons, L'uJ Lditiou, vol. ii. figs. It' J {\>. \i\j'J) uud 107 (p. '•ii'd). 



