128 UniversUy of California Puhlications in Anatomtj [Vol. 2 



pole of the occipital lobe behind the calcarine fissure. This same por- 

 tion of the striate area when destroyed is followed by degeneration 

 of the intermediate segment of the external geniculate body, where, 

 according to Brouwer and Zeeman, macular fibers of the retinae termi- 

 nate. (In Experiment V-c the six small lesions of the occipital oper- 

 cula caused degeneration in the intermediate segments of the external 

 geniculate bodies, figs. 17, 18; in Experiment V-b where only the 

 upper and lower lip of the calcarine fissure was damaged this par- 

 ticular segment remained almost intact, figs. 14, 15, 16; see also 

 Heuven.) The conclusion from the present experiment is, that the 

 macular portion or segment of the visual radiation — the so-called 

 "macular bundle"— runs in an isolated way from its origin in the 

 external geniculate body to its termination in the macular portion of 

 the striate area. It is probable, however, that the actual macular 

 portion of the visual radiation in the monkey is slightly larger than 

 determined here, especially dorsally, since in the most dorsal portion of 

 the macular cortex most of its fibers remained normal. It is also 

 clear that the macular fibers strictly avoid both horizontal branches 

 of the visual radiation and do not enter either of the lips of the cal- 

 carine fissure or its bottom, with the exception of the most posterior 

 portion around both the ascending and descending branches. The 

 present experiment by proving in a clear and simple way the true 

 position and the actual course of the "macular bundle" demonstrates 

 not less clearly the fallacy of the concept held by some contemporary 

 investigators : that the macular fibers form either the most dorsal or 

 the most ventral bundle of the visual radiation and that they reach in 

 some unknown and complicated way, perhaps by passing through 

 the fiber layer covering the calcar avis, the macular cortex. 



Of the descending fibers, interrupted in the sagittal strata of the 

 parietal lobe, only those entering the pulvinar of the thalamus and 

 reaching the superior colliculus of the midbrain degenerated. No 

 degenerated fibers were seen to enter the external geniculate body 

 itself, though the sagittal strata were damaged not far from that 

 body. The belief that there exists an extensive fiber system descending 

 from the striate cortex and terminating in the external geniculate 

 body seems to need further experimental confirmation. 



It is well known from comparative studies that in the course of 

 evolution that portion of the striate area of the lower primates 

 covering the lateral face of the occipital lobe— the so-called operculum 

 occipitale (Brodmann) — was gradually pushed back and inward and 



