CEREBRAL COMMISSURES IN THE VERTEBRATA. 475 



mainly with tlic brain u\' a Lizard {Sccloporiis), a Snake wiiicli lie does uot name, and a 'i'nrtle (As/ndo- 

 vectes). In the Lizard, he says (p. 15), tliere is in the occipital lobe "an undoubted horaologue of the 

 hip])ocampus." Li the Snake he says that " the portion liomologous to the hij)poeainpus is relatively 

 highly ditl'crentiated " ; and that even "the portions corresi)onding in cellular structure to the fornicate 

 and uncinate i^-yri may be distinguished " ! By these statements, which are nonsense as they stand, the 

 author really means to record a would-be important fact. In a later communication upon the brain of 

 DideljJiys (" The Cerebrum and Olfactories of the Opossum," Journ. of Comp. Neurology, vol. ii. 1892) 

 the author calls the fascia dentata the "gyrus uncinatus," the hippocampus the " gyrus fornicatus," 

 and the hip])ocami)al fissure the " splenialis fissure." The monstrous nature of such use of well-known 

 terminology does not seem to have been a])preciated by their author, for when Dr. Hill called his 

 attention to the unusual application of these terms he naively remarked that "obscurity was needlessly 



introduced by using the terms t/i/rns fornicatus and uncinutus for parts which are more 



often named cornu Aminonis and fft/n/s dentutus respectively, without discussion of homologies 

 concerned" (Journal of Comp. Neurology, vol. iii. (1893) ! In the light of these remarks it is possible 

 to understand his statement of 1891, which I have already cpioted above. According to this inter- 

 pretation, it is possible to distinguish in the hippocampus of the Black Snake a marginal region 

 corresponding to the fascia dentata and another region corresponding to the hippocampus (sensu 

 stricto). 



In this (1891) memoir, Merrick gives a good description of the cephalic portion of the real hippo- 

 campus, which he calls " fronto-median lobe " (p. 18), since he does not recognize its hii)[)ocampal 

 nature. This is very surprising, because he records the fact that the so-called " occipital cortex " (which 

 he regards as the whole of the hippocampus) and his " fronto-median lobe " are not only continuous, 

 but pi-csont similar histological features. He does not hint at the fact that the " fronto-median lobe " 

 may also be hippocampus : and his apparent ignorance of the earlier memoirs of Spitzka, Edinger, and 

 Brill exiilains the lack of the suggestion from outside sources, which his own iiistological studies should 

 have supplied. 



The reasons which dictate this distinction between the caudal and the cephalic regions of one uniform 

 and indivisible histological formation are probably to be found in the fact that the caudal portion 

 corresponds in its topographical position to the hippocampus in most Mammals. Yet, strange to relate, 

 neither the study of Didelpliys nor the knowledge of the work of Edinger and others appear to have had 

 any influence upon Herrick's interpretation; for, in spite of the fact that the hippocampus extends 

 forward in the ^larsupial, and in spite of the suggestions of Edinger regarding the hippocampus in 

 Reptiles, he, in his later works, still clings to his original view that it is confined to the caudal part of 

 the hemisphci'e. And for this reason it is not surprising to find that, after deujnng in a positive and 

 formal manner the hippocampal nature of his "fronto-median lobe," he regards its commissure as the 

 true corpus callosum — for this is the natural and logical inference to be drawn from his erroneous 

 interpretation. 



In 1893 Edinger returned to the discussion of the problem of the hippocampus in the Keptilia*, and 

 practically renounced the view (undoubtedly correct) which he had published in 1888. In the later 

 work he attempted to extend the region of the hippocampus to the lateral aspect of the hemisphere in 

 the Chelonia, being apparently deceived by the spurious resemblance of an inverted cortical area in this 

 situation to the Mammalian hippocampus. Not only did he commit this extraordinary error, but also 

 the less excusable one of locating the fascia dentata upon the lateral aspect of the hemisphere external to 

 the Idjjpocampus (cornu Ammonis). It is only just to add tJiat he subsequently appreciated the ground- 

 lessness of these suggestions, and amply acknowledged his error (Abhandl. d. Senckenberg. Gescll. 

 l89G,p. 326). 



* L. Edinger, " Eeichapparat und .immonshorn," Auat. Anzeiger, Bd. viii. 



