GENERAL FEATURES 359 



anterior end, which is called the frontal pole, and the more 

 pointed posterior end, called the occipital pole, and he cannot 

 fail to note that the surface of each hemisphere, at which 

 he is looking, is convex and is directed upwards and later- 

 ally, and may therefore be termed the supero-lateral surface, 

 and he will note, further, that it is moulded into numerous 

 curved ridges of cerebral substance. The ridges are called 

 gyri, and they are separated more or less completely from 

 one another by narrow depressions, some of which are called 

 sulci and others fissures. All the fissures and some of the 

 sulci are named, but there are many small unnamed sulci. 



A mere glance will convince the dissector that the majority 

 of the gyri, at which he is looking, run antero-posteriorly, but 

 that two gyri on each side, which lie a little posterior to the 

 centre of the antero-posterior length of the hemispheres, have 

 an entirely different direction ; they run obliquely from below 

 upwards and backwards. They form, therefore, distinct 

 landmarks ; they are known as the anterior and posterior 

 central gyri, and the cleft which lies between them is called 

 the central sulcus (Figs. 135, 137) (O.T. fissure of Rolando) ; in 

 the majority of cases its upper end cuts the upper or supero- 

 medial border of the hemisphere. 



Between the upper end of the central sulcus and the 

 occipital pole of the hemisphere, but nearer the latter than 

 the former, a deep cleft cuts the supero-medial border of 

 the hemisphere, and extends for a short distance, laterally, 

 on the supero-lateral surface ; it is the lateral part of the 

 parieto-occipital fissure (Fig. 137). 



The dissector should, if possible, insert the brain, or the 

 model with which he is working, into a sagittal section of a 

 skull of convenient size, and note that the upper end of the 

 central sulcus corresponds with a point on the vertex of the 

 skull which lies 12 mm. (half an inch) behind the centre point 

 between the root of the nose and the external occipital pro- 

 tuberance, the nasion arid the inion respectively, and that 

 the parieto-occipital fissure is placed about 6 mm. in front of 

 the lambda. 



When the dissector has satisfied himself regarding the 

 points mentioned, he should examine the supero-lateral 

 surface of the hemisphere from the lateral side. Again he 

 will note the general antero-posterior direction of the gyri and 

 sulci, and the markedly different direction of the central 



