152 THE CEREBRAL HEMISPHERES. 



EXTERNAL SURFACE. The bounding sulci of the external surface of the occipital 

 lobe are, as we have seen, the external part of the parieto-occipital, the anterior 

 occipital, and the lateral occipital. The parieto-occipital has already been described 

 (p. 143). The anterior occipital sulcus (transverse occipital of Ecker) is a 

 transverse furrow, which is laid down as a distinct sulcus in the foetus, but is later 

 almost invariably joined by the horizontal part of the intraparietal, of which it 

 then appears to be the bifurcated posterior end (p. 150). In Quadrumana it is 

 concealed by the occipital operculum, but on drawing this aside it may still be seen 

 at the bottom of the " Affenspalte." It approaches the mesial border of the hemi- 

 sphere above, behind the parieto-occipital fissure, from which it is separated by an 

 annectent gyrus which joins the occipital lobe with the superior parietal lobule. 

 Its lower end, which is often curved forwards, is usually separated from the lateral 

 occipital by the inferior parieto-occipital annectent gyrus uniting the occipital 

 lobe with the postparietal gyrus. In the brain figured (fig. 101), this second 

 occipito-parietal annectent lies deeply, and the two fissures are superficially 

 joined. 



The lateral occipital sulcus runs somewhat obliquely upwards and back- 

 wards from a short distance below and in front of the lower end of the anterior 

 occipital towards the occipital pole of the hemisphere. But before reaching the 

 pole it generally bifurcates in a Y, one branch curving upwards into the occipital 

 lobe, the other downwards towards the posterior end of the calcarine ; it may be 

 embraced by the bifid extremity of the latter. Around its end a lateral occipito- 

 temporal annectent gyrus curves, uniting the occipital lobe with the third temporal 

 gyrus. Within the limits of the occipital lobe as here defined there are usually two 

 or three small sulci of varying extent. These are, however, not constant enough in 

 position and direction to serve for marking out this surface into distinct gyri. 



The external surface lias usually been described (e.g., in previous editions of this work) as 

 having three gyri, a superior, middle and inferior. But this description does certainly not hold 

 good for most brains, and if any division is to be made it must be into anterior (between the 

 anterior occipital sulcus and the upturned end of the lateral occipital) and posterior (behind 

 the upturned end of the lateral occipital). 



MESIAL SURFACE.- The mesial surface of the occipital lobe is occupied by a 

 well-marked gyrus termed the cuneate lobule (cuneus) (fig. 102). This is of u 

 triangular shape, and is bounded in front by the parieto-occipital fissure, and below 

 by the calcarine, while above and behind it reaches the margin of the hemisphere 

 and is continuous with the external surface. It is indented by two or three shallow 

 vertical sulci. 



The parieto-occipital and calcarine fissures which bound the mesial surface have 

 already been described, as well as the deep annectent gyri which pass across them 

 and connect the cuneus with the adjacent lobes (see p. 144). 



The superior longitudinal venous sinus in passing downwards causes an impression on the 

 inner side of the occipital pole of the hemisphere (Bastian). This impression is generally 

 found on the right side, but sometimes on the left. 



According to the usual description, which has been followed in previous editions of this 

 work, the occipital lobe has a tentorial surface, comprising the lingual gyrus and posterior 

 part of the occipito-temporal gyrus (fusiform lobule), which run in a sagittal direction, and 

 are separated from one another by the posterior end of the collateral fissure. But by confining 

 the occipital lobe to the limits above assigned, these gyri and sulci become entirely included 

 in the temporal lobe, along with which they will accordingly be described. 



TEMPORAL LOBE. The temporal or temporo-sphenoidal lobe is bounded 

 above for two-thirds of its length at first by the stem and afterwards by the 

 posterior limb of the fissure of Sylvius, which separates it from the frontal and part 



