MORPHOLOGY OF THE FOREBRAIN 425 



the frog and probably also in Amblystoma. The fibers of the 

 commissura pallii anterior (com. hippocampi) also reach all parts 

 of the primordium. 



Farther caudad in the fimbria complex the commissural fibers 

 predominate. Unmedullated fibers of the commissura pallii 

 anterior come in about equal numbers from the primordium hip- 

 pocampi in front and from the posterior pole. The commissure 

 passes down behind the interventricular foramen to cross in the 

 dorsal part of the commissural ridge of the lamina terminalis 

 (fig. 16). It is the "dorsal commissure" or the dorsal component 

 of the anterior commissure of the older literature and the " cor- 

 pus callosum" of Osborn and his followers. 



The "dorsal commissure" and the ventral or anterior commis- 

 sure are not so clearly separate in urodeles as in the frog and com- 

 parison with the latter type shows that some of the components 

 of the dorsal commissure of urodeles are dissociated from it in 

 Anura. Morphologically the dorsal commissure, or commissura 

 pallii anterior, should be defined as containing only fibers which 

 connect with the dorsal part (pars pallialis) of the hemisphere, 

 and all fibers related only with the ventral parts of the hemi- 

 sphere should be classed with the anterior commissure regardless 

 of their topographic position in the commissural complex at the 

 median plane. 



In the region where the dorsal commissural fibers descend into 

 the commissure ridge of the lamina terminalis an important 

 component of the fimbria complex continues directly caudad 

 to enter the stria medullatis of the same side. The relations here 

 are very intricate, as will appear beyond. This connection lies 

 dorsally of the interventricular foramen, but ventrally of the 

 sulcus medius, i.e., intheparsventralis thalami, and it occurs in the 

 same relations in Anura also. In Amnio ta the configuration of 

 the parts is so modified, chiefly by the posterior chorioidal fold, 

 as to render such a connection impossible. 



At the point where the taenia fornicis joins the taenia thalami 

 the dorsal parts of the hemisphere are cut off from the pars 

 dorsalis thalami and epithalamus by the di-telencephalic fissure 

 and the dorsal plexuses (paraphysis, etc. For the relations of 



