92 



That part of the lamina terminalis, which Burckhardt ^) has 

 distinguished as the "lamina infraneuroporica", contains in the Mono- 

 tremata, Sauropsida and higher Ichthyopsida, two simple commissural 

 bands, which, considering the widely different arrangement and appear- 

 ance of the connected parts in this large series of animals, present 

 remarkably uniform features. The ventral band is the anterior com- 

 missure — the cerebral commissure par excellence — and is distin- 

 guished by the fact that it always passes below the lateral ventricle. 

 In Ornithorhynchus the dorsal commissure connects the hippo- 

 campi majores, fasciae dentatae, and precommissural areae ') of the 

 two hemispheres and may be appropriately distinguished as the fo mix- 

 commissure. In Reptiles the dorsal commissure connects parts of the 

 cerebrum, which, from their histological features and developmental 

 history, are readily recognised as the homologues of the structures 

 connected by the upper commissure in the Monotreme. There is 

 therefore, every reason for calling the dorsal commissure in Reptiles 

 the fornix-commissure. The hippocampus in the latter, in addition to 

 forming (with the precommissural area and fascia dentata) the greater 

 part of the mesial surface, also extends on to the dorsal aspect of 

 the cerebrum, as Edinger ^) and Meyer *) among others, have shown. 

 It is not confined to the posterior part of the hemisphere as Herrick 

 believes^). The fornix commissure in Reptiles is therefore placed 

 above the lateral ventricle. In the vertebrate series this commissure 

 is essentially supraventricular, and its various modifications in 

 lower Vertebrates has been clearly traced by Osborn^) under the 

 name of corpus callosum. Among Amphibia, in spite of many apparent 

 difierences, the same essential features are presented by the two com- 

 missural bands. The dorsal supraventricular commissure connects two 

 regions, which must be homologised with the hippocampus and pre- 

 commissural area. The latter — the "intraventricular lobe" of Herrick, 

 the "callosal eminence" of Gage') — is a very extensive area, with a 

 relatively very large commissural tract. The hippocampus is a large 

 dorsal grey mass of very simple histological structure, but about 

 whose homology there can be no question. The varying relation of 



1) Anat. Anz., Bd. IX, p. 152. 



2) Anat. Anz., Bd. X, No. 15, p. 470. 



3) Anat. Anz., Bd. VIII, No. 10. 11. 



4) Zeitschr. f. wiss. Zoologie, Bd. LV. 



5) Journal of Comp. Neurology, Vol. III. 



6) Morph. Jahrb., Bd. XII. 



7) quoted by Fish. Journal of Morphology, Vol. X, Part 1. 



