1884.] 



On the Human Corpus Callosum. 



349 



February 28, 1884. 



THE PRESIDENT in the Chair. 



The Presents received were laid on the table, and thanks ordered 

 for them. 



The following Papers were read : — 



I. "On the Structure and Functional Significance of the 

 Human Corpus callosum." By Professor D. J. HAMILTON. 

 Communicated by Professor Huxley, P.R.S. Received 

 February 23, 1884. 



Summary. 



1. The results have been obtained by a special mode of preparation 

 formerly described by me. 



2. The fibres in the tip of the frontal lobe run almost directly 

 backwards. A short way behind this they become concentrated in 

 an oval shaped area. This oval shaped area still further back divides 

 into three distinct bundles, and these bundles I have named the 

 tr actus internus, tr actus medius, and tr actus externus. 



3. The tractus internus becomes the corpus callosum and contains 

 two sets of fibres, namely, (a) those coming from the opposite frontal 

 lobe across the corpus callosum, and (b) those going from the 

 frontal lobe of the same side. The fibres which come from the 

 opposite frontal lobe anteriorly do not, after crossing in the corpus 

 callosum, proceed to a corresponding situation on the other side, but, 

 after arching forwards, so as to circumvent the anterior horn of 

 the lateral ventricle and the head of the caudate nucleus, turn back 

 to form the tractus medius and externus. 



4. The tractus externus further back divides into the " inner " and 

 " outer capsules," while the tractus medius joins with the inner 

 capsule shortly after it is given off from the tractus externus. The 

 fibres so derived from the frontal lobe of the opposite side are con- 

 ducted along with the common fibres of the "inner capsule" to the 

 following destinations. Some of them (a very few twigs) end in the 

 head of the caudate nucleus, while the bulk of them are destined to 

 become attached to the thalamus opticus. One large mass derived 



