BY N. DE MIKLOUHO-MACLAY. 195 



stretching the crura cerebri, &c., &c.J After these preliminary 

 explanations I shall proceed to make a few remarks in explanation 

 of the adjoining figures on plate XXIV. 



Already the first examination of the brain at Mabiak showed 

 me after the removal of the very thick pia mater, that the surface 

 of the hemispheres was smooth, without convolutions, with the 

 exception of a transversal depression on the sides in the middle 

 of the hemispheres and a deep fissure corresponding more or less to 

 the fissura Sylvii. These fissures are short and difierently shaped 

 on the two sides. (Fig. 1 and Fig. 2.; Examined from below 

 there are two other sulci, the sulci olfactorii running obliquely 

 forward and covered with the broad tracti olfactorii. 



Horizontal sections of the hemispheres show thin walls and 

 extensive lateral ventricles, the lumen of which has been, in the 

 specimen in question, very much reduced by collapsing of the thin 

 walls. It is only a result of the mode of preservation : should the 

 brain have remained in the cranium in situ, the walls of the 

 hemisphere would have kept their shape, maintained in their 

 natural position by the membranes and blood-vessels of the brain. 



I have specimens of sections of difi"erent brains in situ in the 

 skull which have kept for years their shape and very nearly their 

 size. 



The corpus callosum covers the thalami optici (fig. 3), the 

 columns of the fornix, the septum lucidum (1) and the hippo- 

 campus major are well developed. The anterior white commissure 

 is not large but quite distinct. The upper surface of the compara- 

 tively big thalami optici with a large commissura mollis are 

 covered with the ample folds of the choroid plexus which is closely 

 connected with the epithelium of the third ventricle. (Fig 2.) 



The anterior tubercle and the pulvinar are separated by a 

 distinct oblique groove. 



(1) In my notes made at Mabiak, I find no mention of a ventricle of the 

 septum lucidum and at present it is impossible to decide with certainty 

 about its prior existence and extent. 



