THE CEREBRUM 415 



lobe ; the remainder forms the infero - lateral border of the 

 hemisphere, in the temporal region, and a part of the lateral 

 surface of the temporal lobe. 



Lobus Occipitalis. The occipital lobe forms part of the 

 supero-lateral, part of the inferior, part of the medial surface of 

 the hemisphere, and the occipital pole. Its medial surface, 

 which will be seen more clearly at a later stage, is definitely 

 separated from the medial surface of the parietal lobe by 

 the parieto-occipital fissure. The boundary which separates 

 its supero-lateral surface from the adjacent parts of the parietal 

 and temporal lobes is the small, lateral part of the parieto- 

 occipital fissure, and a line drawn from that fissure to the 

 pre-occipital notch on the infero-lateral border of the hemi- 

 sphere. It is, therefore, largely artificial; and there is no 

 natural line of demarcation between the inferior surface of the 

 occipital lobe and the inferior surface of the temporal lobe 

 (Figs. 138, 156, 159). 



The Sulci and Fissures of the Supero-lateral Surface of the 

 Occipital Lobe. On the posterior part of the supero-lateral 

 surface of the occipital lobe is the terminal part of the cal- 

 carine fissure which curls round the occipital pole, from the 

 medial to the lateral surface. The portion of the brain 

 cortex which immediately surrounds the extremity of the 

 calcarine fissure is part of the striate or visual area of the 

 cortex (Figs. 152, 154, 155). 



Immediately anterior to the end of the calcarine fissure is 

 a curved sulcus, convex forwards, called the sulcus lunatus. It 

 forms the anterior boundary of the visual area on the supero- 

 lateral surface of the hemisphere. Anterior to the sulcus 

 lunatus, and at right angles with it, is the sulcus occipitalis 

 lateralis, which divides the larger, anterior part of the supero- 

 lateral surface of the occipital lobe into an upper and a lower 

 portion. Passing backwards from the parietal lobe into the 

 upper portion of the occipital lobe is the sulcus par-occipitalis. 

 It ends posteriorly in a sulcus, the sulcus occipitalis transversus, 

 which is at right angles with the sulcus par-occipitalis. In 

 some cases a small sulcus, the sulcus occipitalis paramedialis, 

 is recognisable, parallel with and close to the supero-medial 

 border of the occipital lobe (Figs. 152, 154). When it 

 is present the supero-lateral surface of the occipital lobe 

 is separated, by it and the lateral occipital sulcus, into 

 superior, middle, and inferior gyri. 



