340 H. B. POLLARD. 



In front of it is situated the pineal organ, which has a slight 

 cavity. Below the pineal organ lies the cavity of the fore-brain ; 

 below the latter, the massive corpus striatum. The cavity 

 of the fore-brain is continuous with the recessus opticus. A 

 slight distance in front of the ventral limit of the recessus 

 opticus is seen the anterior commissure ; behind it the optic 

 chiasma, for the optic nerves are formed between the third and 

 sixth day, dating from the first day described. The infun- 

 dibulum is seen to be very large. Below it the hypophysis is 

 already formed and in situ. The cavity of the infundibulum 

 shows two smaller cavities proceeding slit-like outwards. The 

 anterior becomes later the cavity of the saccus vasculosus. 

 The posterior is the cavity of the lobus inferior. The axis 

 of the brain-cavity may clearly be seen to be bent like a shep- 

 herd's crook, and to terminate in the region below and behind 

 the anterior commissure. Examining a transverse section in 

 the region of the mid-brain, a very clearly marked crucial lumen 

 is seen to divide the brain into four quadrants. The upper 

 laterals evidently correspond to the '' Flugelplatten " of His, 

 and the lower laterals to the " Grundplatten." The nucleus of 

 the oculo-motor nerve lies in the lower lateral quadrants, and 

 the upper forms the torus longitudinalis. 



The characteristic crucial lumen may be traced con- 

 tinuously forward round the curve of the cranial flexure 

 in such a manner as to indicate that the brain axis ends at the 

 above-mentioned point. In a model of the cavities these 

 relations are especially clear. Thus in its morphological dis- 

 position the corpus striatum corresponds in the fore-brain with 

 the torus longitudinalis, while the wall of the infundibulum 

 corresponds with the region which gives rise to the oculomo- 

 torius in the mid-brain. 



The wall of the infundibulum, however, does not give rise 

 to motor nerves. 



The position of the neuropore and termination of the neural 

 axis in Vertebrates has been the subject of great discussion. 

 The various views have been well summed up by Kupflfer in a 



