THE FOEM-KELATIONS OF THE HUMAN BRAIN. 



189 



The roof of the midbrain commences behind the pineal body. The 

 eommissnra posterior, the crura of which pass backward through the mid- 

 brain, is regarded as the most anterior portion of its roof. The corpora 

 quadrigemina, appearing just behind this commissura, will be considered 

 more closely later. 



Only the mesial portion of the corpus striattim, the nxicleus caudatus, 

 is visible if the brain is opened, as has just been done, from above down- 

 ward. The lateral portion, the nucleus lentiformis, lies deeper and is 



Fig. 127. — Frontal section through the brain of the adult. Explanation in the text. 



covered by the medullary masses passing over it into the capsula interna. 

 It could be exposed by opening downward outside of the nucleus caudatus. 

 A better idea of its form is obtained, however, by making a frontal section 

 transversely through the entire brain at the point in Fig. 125 where the 

 thalamus begins, just behind the thickest part (caput) of the nucleus cau- 

 datus; that is to say, just posteriorly to the ascending pillars of the fornix. 

 It is not very difficult to understand the section (Fig. 137) made in this 

 manner, if the relations shown in Fig. 33 are borne in mind. The wall of 



