NERVOUS SYSTEM. VEBTEBRATA. 163 



deepest and most constant is a short oblique furrow situated 

 just above the mid-point of the anterior rhinal sulcus 

 (i. e., the anterior horizontal part of the rhinal). It 

 represents the presylvian sulcus, which is one of the most 

 constant features of the mammalian neopallium. There 

 are many reasons for regarding this presylvian sulcus as 

 the earliest form of the sulcus known in Human Anatomy 

 by the name "orbital." [Compare the account of the 

 Prosimian brain.] 



Behind the upper extremity of this sulcus there is a 

 shallow transverse depression (figs. 45 & 47, x), which is of 

 interest because the brain of Tlnyladnus, the large relative 

 of Sarcophilus, exhibits a deep sulcus in the corresponding 

 position. 



Above and parallel to the posterior rhinal fissure there 

 is a short horizontal sulcus, and in front of it a small 

 triradiate sulcus (Y). These clearly represent the great 

 sulcus, which I have distinguished as " horizontal " in the 



ventricle and thus produces the calcar avis) is undoubtedly a definite 

 morphological feature, which is the common .property of the Meta- and 

 Eutheria. Yet in the Carnivora, Ungulata, and many other mammals its 

 ventral end may be prolonged almost or quite as far as the rhinal fissure, 

 merely because the expanding cortex in this region is most readily accommo- 

 dated by the extension of this already-existing sulcus. In the Carnivora 

 and Ungulata the upper end of the calcarine sulcus becomes confluent 

 with the intercalary sulcus, forming the so-called " splenial." In the 

 Primates the lower end of the calcarine sulcus does not become prolonged 

 and the upper (posterior) end joins, not the intercalary, but the postcalcarine 

 sulcus. Now, in such a catalogue as this, it is quite impossible to explain on 

 every occasion whether it is the " calcariiie," or the " prolonged calcarine," 

 or a " calcarine complex " to which we refer, without endless confusing 

 periphrases, which would make the accounts hopelessly involved. The same 

 kind of misunderstanding might arise also in the case of the suprasylvian, 

 lateral, or orbital sulcus. 



The reader must therefore bear in mind that the same names are employed 

 in different Orders in order to indicateas concisely as possible where to look 

 for the homologous sulci, rather than to suggest the identity of the whole of 

 any sulcus called by any given name. 



It is also impossible to discuss in a catalogue of limited dimensions all the 

 reason 3 which have led to the adoption of the views set forth in the brief 

 accounts of the various specimens. 



The student who is not acquainted with the nomenclature used for the 

 sulci is referred to the figures of the brain in the Carnivora (infra}. 



M2 



