THE BRAIN 139 



2. Transverse fibres, connecting the two hemispheres : 



(a) Of corpus callosum. 



(b) Anterior commissure. 



3. Collateral fibres, connecting different parts of the same 

 hemisphere. 



(a) Fornix. 



(b) Ttenia semicircularis. 



(c) Nerves of Lancisi. 



(d) Gyrus fornicatus, the fibres of which are said to 



encircle the corpus callosum, near the middle 

 line, meeting at the anterior perforated space. 



(e) Uncinate fasciculus, a white bundle at the bottom 



of the Sylvian fissure, uniting the frontal and 



temporo-sphenoidal lobes. 

 (/) Inferior longitudinal fasciculus, a collection of fibres 



passing between temporo-sphenoidal and occipital 



lobes. 

 (g) Association fibres, passing between and connecting 



together the different convolutions. 



THE MEMBRANES OF THE BRAIN, OR MENINGES. 



The DURA MATER, the most external, is a dense fibrous 

 membrane, which is closely attached to the bones of the 

 skull, forming their internal periosteum. The inner surface is 

 smooth, and covered with endothelium. It is continuous with 

 the dura mater of the spinal cord through the foramen magnum. 

 The fibrous part of the dura mater is divided into two layers, 

 an outer, forming the periosteum, and an inner, lying under 

 the endothelium, forming certain processes, and which, by its 

 separation in certain situations, forms the sinuses (for sinuses 

 of dura mater, vide p. 97). On the upper surface, near, and 

 projecting into the longitudinal sinus, are the Pacchionian 

 bodies, which are enlarged villi of the arachnoid projecting 

 through the layers of dura mater. 



Processes of the dura mater : 



The falx cerebri : placed vertically between the two hemi- 

 spheres of the cerebrum, attached in front to the crista galli, 

 behind to the upper surface of the tentorium, and between 

 these above to middle line of internal surface of skull, while 

 the lower border is concave and free. In relation with it are 

 the superior and inferior longitudinal, and the straight sinuses. 



The tentorium cerebelli is a crescentic fold of dura mater 

 placed between the cerebrum and the cerebellum. It has an 

 outer convex border, by which it is attached in front to the 



