658 



THE NEEVOUS SYSTEM. 



r Olfactory bulb 



The remainder of the true temporal region is composed of an extensive district 

 below the superior temporal sulcus. It is composed of thicker cortex than the 

 superior temporal area, ranging from 3 mm. just below the superior temporal 

 sulcus to 2-5 mm. at the inferior border of the hemisphere. It is composed of 

 three bands of different texture, the middle temporal gyrus, the inferior temporal 

 gyrus, and the pararhinal gyrus, which fringes the area piriformis on the tentorial 

 surface. Upon the lateral aspect of the temporal region a series of irregular 

 furrows are situated along the line of demarcation between the gyrus temporalis 

 medius and the gyrus temporalis inferior ; they are considered to represent a sulcus 



temporalis medius, but 

 they are subject to much 

 irregularity, especially in 

 highly developed brains. 

 The sulcus temporalis in- 

 ferior, which forms the 

 line of demarcation be- 

 tween the gyrus tempor- 

 alis inferior and the gyrus 

 suicus orbitaiis fusiformis, is placed upon 

 the inferior aspect of the 

 temporal region. 



The great extent of 

 the middle and inferior 

 temporal gyri constitutes 



- - Area piriformis one of the outstanding 

 features distinctive of the 

 pararhinai gyrus human brain. Flechsig 

 has shown that the fibres 

 passing to and from these 

 two gyri are the last to 

 become medullated, later 

 even than the important 

 parietal and frontal areas. 



- - optic chiasma 



temporal sulcus 

 (posterior part) 



*:*& 



Fronto-marginal area 



Orbital area 



Pronto-marginal area 



Inferior frontal gyrus 



Area temporalis polaris 



Inferior 



temporal gyrus 



Inferior 



temporal sulcus 

 (anterior part) 



k Sulcus cal- 

 'carinus 



Area temporo- 

 occipitalis 



Sulcus collateralis trans- 

 versus 



Area parastriata 

 Area striata 

 Area peristriata 

 ^. 



Sulcus col- 

 lateralis 



THE VISUAL AEEAS 

 AND FIBEE-TEACTS. 



Area peristriata - 

 Sulcus lunatu 



Sulcus calcarinus lateralis _ 



Sulcus polaris 

 inferior 

 Sulcus calcar- 

 inus posterior 



- Area striata 



FIG. 585. CORTICAL AREAS on the tentorial and orbital aspects of the 

 cerebral hemispheres. 



We have already seen 

 (Figs. 578 and 584) that 

 each optic tract ends in 

 the lateral geniculate 

 body, the pulvinar of 

 the thalamus, and the 

 superior colliculus. From 

 the lateral geniculate 

 body (and according 

 to most writers the thalamus also, though this is not admitted by all) a tract 

 arises which conveys visual impulses back to the occipital pole of the hemi- 

 sphere. This radiatio thalamo-occipitalis (Gratiolet's optic radiation) is seen from 

 various points of view in the figures mentioned, but it is possible (see Fig. 

 587) to expose it in a section which will display it in its relationship to the 

 rest of the visual path (Fig. 586). 



From this it will be seen that the fibres of the optic radiation, after emerging 

 from the lateral geniculate body, bend backwards in the lateral wall of the ventricle 

 and proceed to an extensive district of thin cortex (1/5 mm. or less in thickness), 

 occupying an area of about 3000 sq. mm. of the medial surface and pole of 

 the occipital area. The cortex in this area is distinguished by the presence of' 



