Internal Fore-Brain Structure

Internal Fore-Brain StructureThe internal structure of the fore-brain is so extremely complex that it is only possible to indicate in broad outline its main masses of groy matter, and its principal fibre systems. Within the fore-brain there are three cavities or ventricles (Figs. 61 and 62).

In the hinder portion is the third ventricle, a vertical median slit, which communicates behind with the aqueduct of Sylvius and through this with the fourth ventricle and the central canal of the spinal cord.

In each of the cerebral hemispheres there is a cavity known as the lateral ventricle; it is prolonged into three diverticula or horns - anterior, posterior, and lateral or descending, respectively - so that the whole cavity is of a triradiate form.

The two lateral ventricles are separated from one another in the middle line by a partition called the septum pellucidum; behind this, they communicate with one another and with the third ventricle through the Y-shaped foramen of Monro.

The septum pellucidum is really a double lamina and the cleft separating the two layers is designated the fifth ventricle; this space has no communication with any of the other ventricles.