586 THE COMMISSURES. 



die cornua of the lateral ventricles. While tracing the fibres of 

 the fornix in this portion of their course, two projections are ob- 

 served which have received the absurd appellation of hippocam- 

 pus major and hippocampus minor, which are usually described 

 as distinct bodies, situated in the descending and posterior cornua 

 of the lateral ventricles. JVhen carefully examined in a brain 

 that has been well hardened in alcohol, the hippocampus major, 

 will be found to consist of cineritious neurine, covered by a thin 

 layer of medullary fibres on its inner or ventricular face. This 

 cineritious neurine is a part of, and continuous with, the external 

 or cortical coat of the cerebrum. The hippocampus is a part of 

 a convolution. The medullary fibres come from the under part 

 of the cerebrum, in various directions, and being collected at the 

 inner edge of this body, form what have been usually called the 

 posterior pillars or crura of the fornix, or the tenia hippocampi, 

 but which we must regard merely as the posterior and descend- 

 ing extremity of the inferior longitudinal commissure. The 

 cineritious neurine over which the fibres of the fornix pass at its 

 anterior inferior, and posterior inferior extremities, is in fact but 

 a continuation of that neurine which forms a part of the hemis- 

 pheral ganglia ; that is, a part of the convoluted surface of the 

 brain, but in this situation covered by the inferior fibres of the 

 fornix or inferior longitudinal commissure. In this mode of in- 

 vestigation the real character of the hippocampus major becomes 

 manifest. 



The hippocampus minor, is in some respects analogous to 

 the hippocampus major, for it is formed by the projection at 

 the bottom of one of the fissures dividing the convolutions at 

 the inner side of the posterior lobe, where it is covered by the 

 posterior fibres of the longitudinal commissure. It differs from 

 the hippocampus major in this respect, that the projection is 

 caused by the central or medullary surface of the convolution, 

 and not by th deep doubling inwards of the two layers as is 

 the case in regard to the hippocampus major. It will thus 

 be seen that the fornix serves to connect together many 

 portions of the hemisphere of the same side, as the corpus 

 callosum does those of the opposite sides. Several other 

 commissures of less magnitude are described in the cere- 



