THE ACOUSTIC AEEA AND FIBKE-TKACTS. 



657 



which are also concerned with acoustic functions, but are related to the acoustic 

 radiation only through t^e intermediation of the area acustica of the transverse 

 gyrus (Figs. 581 and 582). 



These areas may be distinguished as the pars intermedia and pars circumambiens, 

 respectively, of the gyrus temporalis superior. During the sixth month of foetal life a 

 furrow makes its appearance along the line of the inferior boundary of the superior 

 temporal area (Fig. 590). It is called the sulcus temporalis superior. 



At a much later stage of development another furrow (sulcus temporalis 

 anterior) makes its appearance further forwards in the temporal region, as the 

 posterior boundary of the area temporalis polaris;~it often becomes confluent with 



Tuberculum olfactorium 



Olfactory tract | Optic nerve 

 Optic tract [ / ( ' Optic chiasma 



Substantia perforata anterior | / i i Infundibulum 



i / / / / Corpus inamillare 



\ ; / / / f Substantia perforata posterior 



/ / / Oculomotor nerve 

 / / / / Internal capsule 



Jtria olfactoria lateralis upon anterior j 

 ' 



part of piriform area 

 Nucleus amygdalae (cut surface) [ 

 triform area (cut surface) j 

 jimen insulae 



Optic radiation / / 



Stria terminalis . * / ,' 



Caudate nucleus ' / ' 



Lateral geniculate body / 



Brachium coliiculi superioris J 

 Thalamus (pulvinar) 



Medial geniculate body i ! 



Basis pedunculi cerebri | 



Red nucleus 



/ / Optic radiation 

 / Caudate nucleus 



Stria terminalis 



Radiatio thalamo-temporalis (acoustic 

 radiation) passing from the medial 

 genicnlate body into the anterior 

 transverse temporal gyrus 



Substantia nigra 



FIG. 584. INFERIOR ASPECT OP PART OF THE BRAIN. The mesencephalon has been cut across and a great 

 part of the cerebral hemisphere dissected away to expose the acoustic radiation (right side of figure 

 in yellow) passing laterally from the medial geniculate body to the deep surface of the transverse 

 temporal gyri, of which a small part is shown in section. Motor fibres in red ; optic fibres, blue : 

 olfactory, dull yellow. 



the real sulcus temporalis superior, and is usually described as part of it. But it is 

 genetically quite distinct from it (Fig. 581). 



If the area acustica is cut across in a perfectly fresh brain it 'will be found to 

 be composed of a thin layer (1'75 mm.) of cortical gray matter, in which two 

 very dense and fairly broad bands of white matter are visible (Fig. 584). These 

 bands are composed largely of fibres of the acoustic radiation, which have entered 

 the cortex to terminate in it. The superior temporal area is composed of somewhat 

 thicker cortex with two bands which are not so densely white as those of the 

 area acustica. The cortex of the temporal polar area is composed of moderately 

 thick, clear, gray matter in which there is a single, narrow, sharply defined white 

 line. 



43 



