THE STRUCTURE OF THE CEREBRAL CORTEX 265 



been removed on the right side of Fig. 119). In the human brain 

 the cerebral cortex is so greatly enlarged that it overlaps all other 

 structures of the hemisphere. 



The anterior end of the early neural tube is an epithelial 

 plate, the terminal plate or lamina terminalis, which forms the 

 anterior wall of the third ventricle in the median plane. The 

 position of this plate is unchanged throughout all subsequent 

 stages of development (Figs. 46-51, pp. 116-119, and Fig. 119), 

 though the cerebral hemispheres grow forward on each side of it, 

 so that in the adult brain it lies deeply buried at the bottom 

 of the great longitudinal fissure which separates the hemispheres. 



The reflex centers of the two sides of the spinal cord and brain 

 stem are connected by transverse bands of fibers known as 

 commissures, for the facilitation of bilateral adj ustments. There 

 is an extensive series of ventral commissures crossing below the 

 ventricle in the floor of the midbrain, medulla oblongata, and 

 spinal cord, and several smaller dorsal commissures are found 

 above the ventricle. In the diencephalon there is a large ventral 

 commissure associated with the optic chiasma, and a dorsal com- 

 missure, the superior or habenular commissure, connecting the 

 habenular bodies of the epithalamus. The basal parts of the 

 cerebral hemispheres are connected by the anterior commissure, 

 whose fibers cross in the lamina terminalis (Fig. 78, p. 165), and 

 there are two large commissures which connect the cerebral 

 cortex of the two hemispheres. One of these, the corpus callo- 

 sum (Figs. 52, p. 119, and 78, p. 165), connects the non-olfactory 

 cortex (neopallium, p. 217), the other one, the hippocampal 

 commissure, connects the olfactory cortex (hippocampus). 

 The fibers of the hippocampal commissure lie under the posterior 

 end of the corpus callosum in close relation with the fimbria 

 (Figs. 78, p. 165, and 80, p. 170). 



In the smaller mammals the cerebral cortex is smooth, but in 

 the larger forms it is more or less wrinkled, so that the surface 

 is marked by gyri or convolutions separated by sulci or fissures. 

 A more highly convoluted cortical pattern is found in large 

 animals than in smaller ones of closely related species, and in 

 animals high in the zoological scale than in lower species; but 

 the factors which have determined this pattern in each individual 

 species are very complex (see Kappers, 1913 and 1914). The 



