CHAP. XXIII.] Or THE HUMAN BRAIN. 457 



of tlie descending cornu *; and (2) the ' peduncles ' of the Pineal 

 Body, which pass forwards along the Thalamus at the upper limits 

 of the ' third ventricle,' gradually diminishing in size and at last 

 apparently blending with the ' anterior pillars ' of the Fornix near 

 the anterior extremity of each Thalamus.f 



Many other sets of ' commissural fibres ' exist on each 

 side whose office also is to bring different more or less 

 distant Convolutions in the same Hemisphere into relation 

 with one another. Some of the principal of these Com- 

 missures are longitudinal in direction, and are disposed in 

 the following manner : j 



1. A great 'axial longitudinal system' runs through the upper 

 portions of the Hemispheres. It contains fibres from the Occipital 

 and Temporal Lobes which pass on to the tip of the Frontal lobe, 

 receiving or giving fibres along this route to many overlying con- 

 volutions. 



2. The ' longitudinal system of the fasiculus uncinatus ' is a 

 set of fibres situated at a lower level than the former, though it 

 connects the same main divisions of the Hemisphere. Its middle 

 portion, forming the band from which it takes its name, is to be 

 seen on the lateral aspect of the hemisphere, crossing the bottom 

 of the Sylvian fissure from the Frontal to the Temporal Lobe. 

 Anteriorly its fibres pass beneath the Corpus Striatum, whence 

 some proceed to the third frontal convolution, others spread out 

 beneath the orbital convolutions to reach the anterior extremity of 

 the Corpus Callosum and the convolutions at the adjacent margin 

 of the orbital region, though the great majority of the fibres pass 

 on beneath the orbital convolutions to end along the anterior edge 

 of the Hemisphere. Posteriorly, the fibres of the fasiculus unci- 

 natus pass to the tip of the Occipital Lobe and to the convolutions 

 along the lower and outer edge of the Hemispheres, whilst a con- 



* This, therefore, would seem to contain fibres serving to connect 

 two distant portions of the same ' Thalamus ' with one another. 



f As those ' peduncles ' of the Pineal Body are continuous with 

 one another posteriorly, they may form a sort of 'transverse com- 

 missure' for those regions of each Thalamus from which the 

 ' anterior pillars ' of the Fornix proceed. 



J See " Journ. of Mental Science," Ap. 1870, pp. 10-16. 



