474 PROF. G. ELLIOT SMITH ON THE MOEPHOLOGY OF THE 



hemisphere and its relation to the choroid plexus are valid reasons for regarding the cortex in question 

 as the representative of the coruu Ammouis, or hippocampus, of the Mammalian brain. 



Having homologized this caudal portion of the medio-dorsal cortex with the hippocampus, Ediuger, 

 with good reason, did not hesitate to regard the cephalic extension of the same histological formation as 

 also part of the hippocampus. But the amazing feature of Edinger's memoir is that, after having 

 recognized this medio-dorsal cortex as the hippocampus^ the author does not hesitate to call the 

 commissure which is derived from it by the name " corpus callosum." And this name has clearly not 

 been employed in the wider sense as including the hippocampal fibres, because upon page 117 this 

 statement is found : — " Ueber der Commissura anterior liegt (fig. 22) die grosse von Osliorn mit 

 Recht als Balken bezeichnete Mantel-Commissur. Ihre Fasern stammen aus dem Gebiet der grossen 

 Zellen in den dorsalen Wand uach aussen der Ammonsrinde." 



The figure 22, to which Edinger refers, represents all these commissural fibres springing not " aus dem 

 Gebiet nach aussen der Ammonsrinde," but from the hippocampus itself, and, so far as ray own 

 observations go, this figure is perfectly accurate. In other words, the great majority, if not all, of the 

 fibres of the dorsal commissure in the Reptile spring from the hippocampus, and therefore cannot be 

 called " corpus callosum." 



It is perfectly incomprehensible why Edinger, who definitely recognized the hippocampus and the 

 fibres of the dorsal commissure springing from it (as his figm'es clearly show), should have called the 

 commissure " corpus callosum." He seems to have deliberately gone beyond his facts in order to make 

 a spurious pretence of agreement with Osboru. NowOsborn (Morphologisches Jahrbuch, 1887, Bd. xii. 

 cit.) did not for a moment deny the origin of the fibres of his so-called "corpus callosum" from the 

 mesial cortex in the Reptile. The fallacy of his argument was his failure to recognize this mesial cortex 

 as hippocampus. Edinger clearly recognized the latter fact, but failed to see the logical outcome of his 

 suggestion. He seems to have utterly ignored the facts which he had himself clearly demonstrated, for 

 the sake of a pretended confirmation of the conclusions of Osborn. 



Two years after the publication of this memoir of Edinger's, Brill published a brief communication *, 

 with a view to make known the work of Spitzka, and to record a series of original observations upon the 

 brain in the Lacertilia, Ophidia, Crocodilia, and Chelouia. He argued that the position of the medio- 

 dorsal cortex in the hemisphere and its histological structure showed its homology to the fascia dentata. 

 He regarded the rest of the dorsal cortex as the hippocampus and subiculum cornu Ammonis. And in 

 support of this hypothesis he propounded (upon wholly inadequate grounds) the statement that " the 

 fascia dentata is more primitive than the hippocampus," and therefore not unnaturally " forms the greater 

 part of the Reptilian hemisphere." In the introduction to this discussion I pointed out that the fascia 

 dentata is a specialization of the ventral edge of the pre-existing hippocampus, which makes its 

 appearance relatively late in the ontogenetic history of the Mammalian brain. Moreover, it consists of 

 a peculiar modification of the surface (only) of the hippocampus, as I have shown elsewhere ("The 

 Fascia dentata," Anatomischer Anzeiger, Bd. xii. 1896, p. 124.). So that it cannot exist apart from the 

 hippocampus. 



In its typical form the fascia dentata is found only in the Mammalia, whereas the hippocampus can 

 be certainly recognized in all the Sauropsida, Amjjhibia, and Dipnoi, and even in some still lowlier 

 vertebrates. It is therefore preposterous to argue that " the fascia dentata is more primitive than the 

 hipuocampus," as Brill does. 



In 1890 C. L. Herrick began the publication of a series of contributions to the morphology of the 

 brain. The first of these memoirs which deals with the question at issue appeared in the first number 

 of 'The Journal of Comparative Neurology," which this prolific writer founded in 1891. It deals 



* N. E. lirill, " The True Homology of the Mesal Portion of the Hemispheric Vesicle in the Psauropsida [sicV' 

 Medical Hecord, March 29, 1890, pp. 343-345. 



