Dr. Foville on the Anatomy of the Brain. 19 



of those on the left. On each side they seem to pass from the 

 pyramid before to some small columns which proceed from 

 the posterior commissure behind. These two opposed layers 

 of fibres passing from before to behind, correspond in the 

 medulla oblongata to the double band having the same dis- 

 position in the medulla spinalis. 



With the posterior bundles of the medulla oblongata, con- 

 tinuous with the posterior commissure of the spinal marrow, 

 are connected those white fibres seen on the surface of the 

 calamus scriptorius, which are said to go to the auditory nerve. 



I must not forget to say, that from these same posterior 

 ascending bundles proceed radiating fibres, going to the su- 

 perficial columns of the medulla oblongata, in like manner as 

 there are found radiating fibres proceeding from the axis of 

 the medulla spinalis and going to its superficial columns. 



These remarkable anatomical arrangements are not to be 

 found in the spinal marrow and medulla oblongata alone ; 

 they exist still higher, in the crura cerebri. I must not now 

 attempt to describe these connexions further, as I have several 

 other points to notice, and shall therefore be glad if I have 

 succeeded in conveying to you some idea of their character. 

 Nor will I here undertake to describe the multifarious and 

 highly complicated parts which are to be found in and above the 

 medulla oblongata going to the cerebellum and cerebrum, in to 

 which many of them may be followed. I will merely remark, 

 that among all these fibrous bundles those in communication 

 with the anterior pyramids are the most simple and the most 

 direct in their progress to the brain through the crus cerebri, 

 for they constitute the inferior part. 



This inferior part of the crus cerebri, flattened a little 

 transversely at its entrance into the brain, is received into a 

 transverse cavity. 



The superior part of the same crus cerebri when entering 

 the brain unites directly with the thalamus nervi optici, which 

 seems to be an enlargement and modification of this part. 

 When attentively examined, the thalamus nervi optici is seen 

 forming with its appendages, of which the nervus opticus 

 emerging from it is the most remarkable, a complete circle, or 

 at least a rounded mass, about the inferior part of the crus 

 at its entrance into the brain. 



It seems highly important to distinguish with exactness the 

 further disposition of these two distinct prolongations of the 

 crus cerebri. 



Internal to the fissure of Sylvius there is an elongated four- 

 sided surface, of whitish colour, which is the only fibrous part 

 of the external surface of the brain. This quadrangle is 



C2 



