Dr. Foville's Researches on the Anatomy of the Brain. 333 



nervorum opticorum, and form a plane of which all the rays 

 tend towards the curved line which limits the corpora striata 

 and thalami on the outer side. 



At this point, to which we have traced the radiating fibres 

 of the crus cerebri, we find the commencement of a different 

 arrangement : but before speaking of this, it will be proper 

 clearly to define whence we are to set out. 



The fibrous expansion of the crus forms in the substance of 

 the corpus striatum and thalamus a large plane directed ob- 

 liquely outwards and upwards. This plane separates the cineri- 

 tious matter of the corpus striatum into two nearly equal por- 

 tions, of which the one rests on the superior face of the plane, 

 and is that which we see projecting into the ventricle ; the 

 other, placed beneath the plane, is as it were lost in the mass 

 of the hemisphere. This broad plane of the corpus striatum 

 and optic thalamus, or in other words the expansion of the 

 crus cerebri, presents nearly the figure of a triangle bounded 

 by two straight lines and a curved one ; the two straight lines 

 are the two sides of the crus, the curved line is the boundary 

 of the corpus and thalamus to the outer side of the ventricle. 

 It is to this curved line as to a circumference that the radiating 

 fibres of the crus are directed. This line, the imaginary limit 

 of the expansion of the crus, we shall assume as the origin of 

 other parts which we are now about to examine. 



From this line, on the outer side, there proceed three per- 

 fectly distant planes or layers placed one above another at their 

 origin, whence each pursues a particular course. 



\st Plane. — The superior plane, which on account of its di- 

 stinction we may call the plane of the ventricle, or the plane of the 

 corpus callosum, arising from the curved line before mentioned, 

 mounts on the outer side of the corpus striatum and thalamus, 

 to which it is applied, having in the first part of its course a 

 nearly vertical direction. It forms a slight convexity outwards, 

 and then bending inwards horizontally towards the median 

 line, unites with its fellow, with which it concurs to form the 

 corpus callosum. 



Thus the corpus callosum as a whole represents a roof, of 

 which the sides proceeding from the plane of the corpus stria- 

 tum and thalamus are continuous with the crura cerebri, and 

 have nothing to do with the hemispheres properly so called. 

 In other wortls, tiie corpus callosum is a true commissure of 

 the crura cerebri. Hut do its fibres pass from one side to the 

 other across the median line? Is there upon this line an 

 auastomosis of fibres? These are questions to which my 

 txainiiialion of this jiart have not vet cnnbleti me to leply. 

 2«rf/'A/«c. — InuHediatclybciiciUlilheplancwhitlnvcliavejust 



examined, 



