NERVOUS SYSTEM. VERTEBRATA. 169 



be regarded as analogous to the " Sylvian fissure" of 

 Carnivores *. 



A deep sulcus (Y) begins near the posterior margin of 

 the hemisphere and pursues a course parallel to the posterior 

 rhinal almost as far forward as the " Sylvian fissure." Its 

 anterior extremity is joined by a shallow oblique sulcus to 

 a second deep furrow (x) which pursues the same direction 

 as the posterior sulcus but on a slightly higher level. The 

 whole complex forms a great sulcus crossing the hemisphere 

 obliquely as far as the dorso-mesial edge, where it almost 

 reaches the upper extremity of the prolongation of the 

 calcarine sulcus (fig. 48) . The determination of the homo- 

 logies o these furrows is fraught with great difficulty ; but 

 it will be found, I believe, that the sulcus Y represents the 

 suprasylvian and the furrow x the coronal sulci of other 

 mammals. In the right hemisphere of a Thylacine described 

 by Beddard the sulci x and Y overlap but do not join. In 

 the left hemisphere of his specimen the condition described 

 in this hemisphere is found. 



In front of the presylvian there is a short separate hori- 

 zontal sulcus analogous to that called " prorean " in the 

 Carnivora. On the left hemisphere it joins the presylvian. 

 There is a shallow olfactory sulcus (i. e. the depression in 

 the neopallium which lodges the olfactory bulb and 

 peduncle.) 



There are also a few ill-defined punctate depressions 

 below and above the x + Y complex sulcus. 



The plan of the sulci is a more complete elaboration of 

 that faintly foreshadowed in the Tasmanian Devil. It has 

 undoubtedly considerably diverged from the plan found in 

 most placental mammals, though not to such a marked 

 extent as that of the Monotremes or even of the Diprotodont 

 Marsupials. 



The optic tract may be seen spreading out on the lateral 

 tubercle of the optic thalamus. Behind tlje latter note the 



* But this is a feature vastly different from the true Sylvian fissure of the 

 Primates (vide infra). In the latter part of this work I have therefore dis- 

 carded the erroneous name " Sylvian " and called it " pseudosylvian." The 

 earlier part was already in print before I fully appreciated the utterly mis- 

 leading effects of calling this furrow " Sylvian." 



