324 DE. G. ELLIOT SMITH ON 



missural area. It forms a broad tract lying in front of the lamina terminalis (l.t.), which 

 contains the anterior commissure : it extends forward to become continuous with the 

 mesial surface of the olfactory peduncle; it is separated above from the pallium by the 

 precommissural vestige of tlie hippocampus {v.h.'), and below it extends into continuity 

 with the tuberculum olfactorium. The dorso-caudal angle of the paracommissural body 

 has been drawn upward and backward as a long pomted process [ji'), which fills up the 

 gap between the psalteriurn {j>s.) and corpus callosum {c.c). Tliis process is somewhat 

 stretched, and is the homologue of the septum lucidum of human anatomy. With the 

 corresponding lamina of the other hemispliere it encloses a narrow median slit — the 

 cavum septi, which opens forward and downward. The only important difference in the 

 Myrmecoijhagidce (fig. 23 A) is that the "septal" part {p.') of the paracommissural body 

 has been stretched to a mucii greater extent. 



In the Armadillos (fig. 23 C) there is practically no septal part of the paracommissural 

 body. 



In the Pangolins the condition most nearly approaches that of the Sloths. 



The Pallium. 



It is convenient for descriptive pui-poses to associate together all the surface-areas 

 which we have so far discussed — bulbus and pedunctiliis olfactorins, tuberculum 

 otfo.ctorium, lobus lyyriformis, lobus perforatus, hij^pocamjms, and area prcccommissuralis 

 — in contradistinction to the rest of the surface of the hemisphere, \\ hich it is customary 

 to call 2)allium.. 



The histological structure and the morphological relations of each of the structures 

 which have just been enumerated are quite distinct, and present little, if anything, in 

 common to those of any of the other areas. But while they present so little in common 

 they are clearly distinguished from the rest of the cortex or pallium by the fact that they 

 are phy logon etically older, and at the dawn of the mammalian epocli had reached the 

 height of their histological difTerentiation and morphological importance. The pallium, 

 on the other hand, is phylogenetically quite recent, seeing that it can be first definitely 

 recognized as a very insignificant element in the cerebral hemisphere of rej)tiles. In the 

 Mammalia for the first time it develops its distinctive features, and continues to increase 

 in morphological importance and in histological elaboration. There is, therefore, a 

 very clear line of demarcation between the behaviour of the pallium attd the rest of the 

 sui'face of the brain which deserves to he clearly i*eflected in any system of nomenclature 

 Avhich we may adopt. From the fact that all the surface-areas, apart from the pallium, 

 are more or less intimately associated with the olfactoiy apparatus, it has become 

 customary to apply the term " rhlnencephalon " to this group of surface-areas. Tliis 

 application of tlie term " rhinencephalon " was suggested by Sir William Turner*, 

 although at that time the exact limits of the region — more especially with regard to the 

 precoii missural area — could not be mapped out. The suggestion of Schtifert to include 



* AV. Turner, op. ril., ' Journal of Anatomy and rbysiology,' voL xxv. 1890. 

 t E. A. Schafer, Quain's 'Anatomy,' 10th cd. vol. iii. part 1, ISO'.i. p. IGU. 



