32 BULLETIN OF THE LABORATORIES 



the thalami, which thrust the adjacent ventral wall inward so as al- 

 most to fill the cavity. That part of the original cavity which is not 

 thus lost is greatly reduced by the adhesion of the dorsal and ventral 

 parts of the wall until only a narrow space remains on either side, the 

 lateral ventricles. The portion of the lower wall which is invaginated 

 appears, when the ventricle is opened, as an arched mass in its floor, 

 the cornu ammonis. This lower wall is not simple, but is convoluted, 

 forming a folded arch directed cephalad, stretched over the thalamus. 

 Thus, imagine that the hollow body [secondary prosencephalic versicle] 

 has had the lower wall on either side driven cephalad by a fold springing 

 from behind in the direction of the arch of the thalamus opticus (Plate 

 III, Fig, 4, a.) By this process there arise a lamina superior and a la- 

 mina inferior cornu ammonis (Plate III, Fig: 3, le and /*.) The terms 

 are strictly applicable in only a part of the course of these bodies, 

 since the relation of the two laminae is altered caudad, the upper be- 

 coming lateral, the lower median. [These two portions are parts of 

 the gyrus fornicatus.] In comparing the Amnion's horn with other 

 parts of the cortex a difference is obvious, especially in the inferior 

 lamina, in that a second fold has taken place, intercalating a band of 

 smaller cells than those of the remainder between the upper and lower 

 laminae. This is the so-called granular layer, or taenia cinerea cornu 

 ammonis of Volkmann [gyrus uncinatus, Plate III, Fig 3, gn.] The 

 two cornua meet and coalesce to some extent in the median line. 

 The connection between the two cornua is chiefly due to the confluence 

 of the layer of fibres and of large cells of the superior lamina. Far 

 cephalad the layers of large and small cells of the inferior lamina also 

 coalesce. The fibres arising in the Amnion's horn of either side arch 

 over the thalamus and converge behind the callosum where they separate 

 from the cornua and plunge obliquely into that part of the substantia 

 cinerea anterior caudad of the collosum and cephalad of the thalamus. 

 "In the region of the anterior walls of the third ventricle these grad- 

 ually diverging bundles disappear behind the anterior commissure. 

 They obviously, therefore, form a longitudinal commissure of the 

 anterior ventral part of the hemisphere, the substantia cinerea anterior, 

 with the posterior portion of the hemisphere. In other words they 

 constitute the fornix." Stieda recognizes two bundles of fibres in the 

 cornu ammonis, one longitudinal, the other transverse, one passing 

 to the callosum, the other to the fornix. In carnivora Stieda states 

 that the gray matter of the two cornua is not confluent. 



