1932] Poliak: Afferent Fiber Systems, Primate Cerebral Cortex 89 



the entire auditory projection cortex. The smallest number of such 

 cortical terminations was found in the region corresponding' with the 

 most anterior segment of the auditory projection cortex. If this be 

 taken as a criterion of the best and of the poorest supply of the audi- 

 tory projection cortex with afferent fibers, its most caudal segment 

 would represent its "focal zone."^ However, even in this focal zone, 

 the wealth of degenerated intracortical afferent fibers is below that 

 found in the "focal zone" of the somatic sensory region around the 

 bottom of the sulcus centralis. (See Chapter VII.) 



It might also be of importance to mention that here, in the cortex 

 of the auditory "focal zone," just as was described for the somatic 

 sensory cortex and for the striate area, the supply of afferent fibers 

 is a continuous one without any visible gaps or zones lacking afferent 

 fibers. This indicates that here as well as in the somatic sensory cortex 

 and in the striate area, there is the same uninterrupted cortical repre- 

 sentation of the peripheral receptive surface (cochlea, skin, retina). 



As to how conditions in the brain of lower primates compare with 

 those known in man, the following may be said : In the sylvian 

 region of the Macacus essentially the same conditions exist as in the 

 human brain, although more simplified. In the most posterior portion 

 of the monkey's Sylvian fossa, there exists an elevation of the cortex 

 of the upper lip of the superior temporal convolution (Ttr) which 

 could well be compared with Heschl's transverse convolution (figs. 30, 

 50, 51, less evident in fig-s. 29, 33). That region actually has, in the 

 present experiments, the best supply of afferent fibers and it might 

 well be a homologue of area TC and TD of Economo-Koskinas. Thus 

 in the monkey there also exists a special portion of the auditory pro- 

 jection cortex well supplied with afferent fibers, entirely, or at least, 

 chiefly hidden in the Sylvian fossa, and comparable to Brodmann's 

 areas 41 and 42 in the human hemisphere, or to Mauss' areas 38 and 

 40 found in the higher apes. Yet it is questionable whether the entire 

 auditory projection cortex as here delimited in the monkey's brain 

 is homologous merely to Brodmann's areas 52, 41, and 42, approxi- 

 mately Economo's area TC of the human brain, or whether it also 

 embraces portions of area 22, and corresponds to areas TA, TB, TC, 

 and TD of Economo-Koskinas taken together, as appears probable. 

 At any rate, it is highly probable from the present experiments that 

 a wide cortical region concerned with the reception of peripheral 

 auditory impulses does not exist, but a comparitively small portion of 



Compare Beck, 1929. 



