460 THE BRAIN 



divided parts, and he should compare the cut surfaces with 

 Figs. 177, 159. 



When the study of the cut surfaces is completed, a horizontal 

 incision must be made through the remains of the right half of 

 the cerebrum, at the level of the upper part of the interventricular 

 foramen, in order to display the relative positions of the basal 

 ganglia. And through the left part of the cerebrum a number 

 of frontal or vertical transverse incisions must be made, the 

 first, immediately in front of the posterior end of the olfactory 

 tract, the second, through the anterior perforated substance ; 

 the third, immediately anterior to the mamillary bodies, and the 

 fourth, through the cerebrum and then through the front part 

 of that portion of the cerebral peduncle which is still attached 

 to it. 



After the sections have been made, examine the horizontal 

 section first(Figs. 182, 183), and note the following points, using 

 the upper surface of the lower segment : (i) The peripheral 

 grey and the central white matter of the hemisphere. (2) 

 Close to the median plane, from before backwards (a) the 

 divided anterior part of the corpus callosum and the fibres of 

 the forceps minor passing forwards and laterally from it into 

 the white matter of the frontal lobe ; (<) the right layer of 

 the septum pellucidum ; (c) the divided right column of the 

 fornix ; (d) the medial surface of the thalamus, separated 

 from the column of the fornix by the interventricular foramen ; 

 (e) medial to the posterior part of the thalamus, the upper 

 surface of the anterior part of the lamina quadrigemina and 

 a part of the pineal body. (3) Lateral to the anterior divided 

 part of the corpus callosum is the cavity of the anterior horn 

 of the lateral ventricle. (4) In the lateral wall of the floor of 

 the anterior horn the divided head of the caudate nucleus of 

 the corpus striatum. (5) Bounded medially by the head of the 

 caudate nucleus and the thalamus, a broad band of the white 

 matter called the internal capsule. (6) Lateral to the internal 

 capsule, a triangular mass of grey matter called the lentiform 

 nucleus. It is divided into three parts by two thin white 

 laminae called the medial and lateral medullary laminae. 

 The most lateral of the three parts is called the putamen ; it 

 is larger and darker than the medial two portions, which 

 form, together, the globus pallidus, which is paler than the 

 putamen. (7) Lateral to the lentiform nucleus, a thin lamina 

 of white matter called the external capsule. It is continuous, 

 anteriorly and posteriorly, round the anterior and posterior 

 margins of the lentiform nucleus, with the anterior and 

 posterior borders of the internal capsule, and it is bounded, 



