FCETUS OF FOUR MONTHS. 597 



yet but little developed. Below is seen the two anterior crura 

 of the fornix, which come up from the eminentia mammjllares, 

 unite slightly together, turn round the thalami, and subse- 

 quently diverging to form the posterior crura of the fornix or 

 corpus fimbriatum, are lost in the lower and posterior part of 

 the hemispheres. On the outer side of these crura there is a 

 doubling inwards of the walls of the ventricles, evidently in- 

 tended to form the hippocampus major, and a corresponding 

 elevation behind, the rudiment of the hippocampus minor. The 

 great cavity in each hemisphere, which forms as yet but one large 

 ventricle, terminates in front in a canal which leads into the 

 cavity of the bulb. The anterior commissure not being formed 

 and the fornix as yet incomplete, there is no separation between 

 the middle and lateral ventricles. The larger part of this cavity 

 is filled up with the plexus choroides. The thalami are about a 

 quarter of an inch long and nearly two lines broad, and seem 

 placed as it were, as a bulbous expansion on the posterior ascend- 

 ing fibres of the crus cerebri. On their upper surface are seen 

 the peduncles of the pineal gland which unite together to form 

 that body. 



The corpora striata, are well formed and smooth, but do 

 not present the striated appearance when divided across. 

 The cerebral hemispheres are about ten lines long and nearly 

 a quarter of an inch broad, and form two sacs, one over each 

 crus cerebri, which are as yet chiefly connected together by the 

 anterior portion of the corpus callosum, and the fornix. The 

 texture of the walls of these hemispheres is now plainly seen to 

 be fibrous on its inner face. On the outer surface the structure 

 though not fibrous, does not yet present any resemblance to 

 cineritious matter. The fibres from the anterior columns of the 

 medulla oblongata may be traced upwards and forwards; at first 

 they are covered and partially interlaid with the transverse fibres 

 from the cerebellum, that are to form in part the future pons 

 varolii ; two membranous processes are then detached upwards 

 on the back of the hollow mass known as that of the tubercula 

 quadrigemina, the larger portion of the fibres of the crus, passes 

 up through the optic thalamus ; some bundles of fibres descend 

 on the inner and lower side of the thalamus to the eminentia 



