162 PHYSIOLOGICAL SERIES. 



In the smaller fia*yimdfe this sulcus is not present. 

 The cranial surface of the hemisphere is not quite smooth. 

 The rhinal fissure separates the pyriform lohe from tin* 



Fig. 47. (Nat. size.) 



neopallium, and in addition the latter is also marked l>y 

 several shallow furrows (figs. 45 and 47). . Of these tin* 



mammal^ ; whereas others go to the opposite extreme and deny in tot<> the 

 possibility of hoiuologising the sulci found in one Order of mammals with 

 those of another. 



There can be little doubt that the fundamental constituents of m:my <>f 

 tli-' sulci found in the Metatheria and Kutheria are morphologically stable 

 elements which can be certainly homologised in many different Orders. 



The exact homology of the hippocampal and rhinal fissures in all mammal- 

 ia beyond question, because the peculiar histological features of the lips of 

 these fissures enable us to certainly identify them. The developmental 

 history and the behaviour of the fundamental constituents of the calcariin 

 sulcus of Primates and the upper part of the vertical minus of tin- siilm 

 commonly called "splenial" in other mammals indicate their identity. In 

 the same manner we can recognise the suprasylvian, lateral, coronal, an.l 

 orbital (presylvian) sulci in the most diverse Orders of mammals. M 

 these names were originally applied to the Carnivora (vide infra). 



' fundamental constituent " I mean the stable basis of a sulcus, which 

 seems to be produced (even when the mechanical conditions must be \ 

 different) in various Orders of mammals in response to some factors other tin n 

 the mere general expansion of the neopallium. The extending cortex ma\ 

 be accommodated in the neighbourhood of such a sulcus by the prolongation 

 of the latter : or, agau<, the furrow in question may become confluent with 

 various other sulci in different mammals. Thus the calcarine sulcus i 

 ttricto, i. e. the short post-splenial furrow, which indents the wall of tin- 



