NATURAL SUBDIVISION OF THE CEEEBEAL HEMISPHERE. 433 



<7) The hippocampal formation, sharply differentiated into (a) 

 the hippocampus (se^isu stricto), and {h) the fascia dentata. 



(8) The corpus striatum ; and 



(9) The rest of the hemisphere, consisting of a dorsal cap 



which is the " neopallium." 



(1) The olfactory bulb calls for no description, because no 

 one can dispute the fact of its peculiarly distinctive histological 

 structure. 



(2) The olfactory peduncle is merely the prolongation back- 

 ward of the innermost layers of the olfactory bulb. 



(3) The olfactory tubercle (figs. 1, 2, 3, and 4) is a peculiar 

 cortex, which forms a cap upon the ventral aspect of the head 

 of the corpus striatum. Its structure is well known from the 

 descriptions of Ganser, Calleja, and others (see Kolliker, Gciuehe- 

 lehre, Bd. ii., 1S96, p. 725). 



(4) The pyriform lobe is a mantle or " pallium " of a struc- 

 ture so peculiarly distinctive that it may be recognised in 

 sections of the brain of any mammal, even when coloured by 

 ordinary nuclear stains. Its features have been well described 

 by Kolliker {op. ciL, 1896, p. 723). The e.xact extent and rela- 

 tions of this " mantle " (I use this term advisedly) are not 

 generally recognised. Its anterior portion is closely applied 

 and attached to the lateral aspect of the corpus striatum 

 (fig. 5), and extends forward so as to pass into direct continuity 

 with the olfactory peduncle, its peculiar structure undergoing 

 a gradual transition into the somewhat indefinite " peduncular " 

 formation ; its antero- ventral part is covered by the thick mass 

 of the tractus olfactorius [lateralis] (fig. 1,4'), radiating fibres of 

 which are spread over the whole of the pyriform lobe. In its 

 caudal part the pyriform lobe becomes free from the corpus 

 striatum, and becomes a real " mantle " (fig. 5), which extends 

 in the caudo-mesial direction to become continuous with the 

 hippocampus.^ 



^ Waldeyer (Merkel and Bonnet's Ergebnissc der AiiaL u. Eiitwick, Bd. viii. 

 for 1898, pp. 372 and 380) objects to my spelling of the word " pyriformis," on 

 the gronnd that a word derived from the Latin " pi I'um" ought not to be 

 spelled with the letter " y." This undoubted philological error, however, is not 

 only shared by most writers of all nationalities, but is so fixed by long usage (at 

 any rate in England), in such terms as " musculus ]iyriforniis," that it would be 

 pedantic at this late hour to attempt to rectify the spelling. 



