ANATOMY AND PHYSIOLOGY OF THE BRAIN : 



the septum lueidum, and each is divided into a body 

 and three eoruna, an anterior, posterior, and middle. 

 The foramen of Monro connects them with the third 

 ventricle. 



The third ventricle is derived from the primitive 

 fore-brain vesicle, except that portion which also 

 enters into the formation of the lateral ventricles. It 

 is a narrow space between the two thalami and hypo- 

 thalamic gray, limited in front by the terma, behind 

 continuous with the aqueduct of Sylvius, and laterally 

 is continuous with the lateral ventricles through the 

 foramen of Monro. 



The fourth ventricle is an irregularly pyramidal- 

 shaped cavity, with a lozenge-shaped base, and ridge- 

 like apex; found between the medulla oblongata and 

 the back part of the pons varolii in front and the 

 cerebellum behind. It is divided into a roof and a 

 floor. Below the fourth ventricle is continuous with the 

 small central canal of the cord and post-oblongata 

 (in part) ; above it communicates with the third 

 ventricle by means of the aqueduct of Sylvius. The 

 fourth ventricle has an opening through the tela 

 choroidea, which permits of communication with 

 the subarachnoid space; it is called the foramen of 

 Majendie. 



THE STRUCTURE OF THE CEREBRUM. It consists 

 of masses of gray and white substance. The gray 

 being outside, makes up the cortex. The gray sub- 

 stance is composed of layers of nerve cells and nerve 

 fibers, with their axones and dendrites embedded in 

 a net-work of neuroglia. The nerve fibers may be 

 amyelinic or myelinic. Their direction may be either 

 transverse or vertical. 



The white substance of the cerebrum is composed 

 of myelinic nerve fibers interwoven into an intricate 

 series of pathways, which are classified into (1) asso- 

 ciation fibers, which connect neighboring or distant 



