120 
tempts at interpreting the region have been mainly based upon the 
elucidation of its fine histology by the GoLe1 staining method by SALA1), 
SCHAFFER”) and Ramon y CasaL*) among others. The difficult task 
of interpreting the maze of the hippocampus in this way has only pro- 
duced uncertain and often conflicting results. By studying the evolution 
of the mammalian hippocampus from its simple reptilian homologue, its 
morphology can be readily and certainly interpreted. Moreover, in the 
cerebrum of the marsupial and monotreme, where no dorsal com- 
missure of the pallium (true corpus callosum) exists to disturb 
its relations, the anterior (dorsal) extremity of the hippocampus Ex- 
hibits in the adult brain, all the different stages (in a series of trans- 
verse sections) from the simplicity of the reptilian to the complexity 
of the eutherian cornu Ammonis. The examination of such a series 
forms the basis of these preliminary notes. The different stages may 
be seen in any adult marsupial or monotreme, but especially well in 
Ornithorhynchus. The study of the development of the region 
in Embryos of Ornithorhynchus, Perameles, Dasyurus and 
the pig fully bears out the facts ascertained by the examination of 
the adult brain. 
SCHWALBE*) regarded the Fascia dentata as constituting with 
the nucleus Fasciae dentatae one convolution, of which the Stratum 
granulosum was compared to the layer of small pyramids of the ge- 
neral cortex. HENLE, KRAUSE, MEYNERT, HUGUENIN and OBERSTEINER 
among others maintain practically the same view. 
DuvaL’), GoLGI®) and Sata’) among others regard the Fascia 
dentata (Stratum granulosum and Str. moleculare) as a convolution 
independent of the nucleus Fasciae dentatae. It will be clearly seen 
in the present paper that the Fascia dentata in this sense cannot 
be regarded as a convolution, and therefore the application to it of 
the name Gyrus dentatus is inaccurate and misleading. 
1) “Zur feineren Anatomie des großen Seepferdefußes”. Zeitschr. f. 
wissensch, Zool., Bd. LII, No. I, 1891. 
2) “Beitrag zur Histologie der Ammonshornformation”. Arch. f. mikr. 
Anatomie, Bd. XXXIX, 1892. 
3) “Estructura del asta de Ammon”. Annales de la Sociedad espa- 
hola de historia natural, Serie II, Tome I, Cuad. IV, 1893. 
4) Lehrbuch der Neurologie. 
5) “La corne d’Ammon”. Archives de névrologie, 1881. 
6) “Sulla fina anatomia degli organi centrali del sistema nervoso”. 
Milano 1886. 
7) loc. cit, 
