The Hemispheres of the Brain

The two hemispheres constitute the largest portion of the encephalon, and together with the parts derived from the thalamencephalon, from what is called by some writers the fore brain. They occupy the whole of the vault of the skull, and consist of a central cavity, in either hemisphere, surrounded by exceedingly thick and convoluted walls of nervous tissue. The under surface or base of the cerebrum is of an irregular form, resting in front on the anterior and middle fossae of the skull and behind upon the tentorium cerebelli. The upper surface is of an ovoid form, broader behind than in front, convex in general outline, and divided into two lateral halves or hemispheres, right and left, by the great longitudinal fissure, which extends throughout the entire length of the cerebrum in the middle line, reaching down to the base of the brain in front and behind, but interrupted in the middle by a broad transverse commissure of white matter, the corpus eallosum, which connects the two hemisphere together.

The surface of the cerebrum

Each hemisphere presents an outer convex surface, filling the concavity of the corresponding half of the vault of the cranium; an inner, flattened surface, which is vertical and directed toward the corresponding surface of the opposite hemisphere (the two forming the sides of the longitudinal fissure); and an under surface or base, of an irregular form, which rests in front on the anterior and middle fossae of the base of the skull, and behind upon the tentorium cerebelli. The hemisphere are composed of an outer stratum of gray matter, called the cortical substance. It is thrown into a number of creases or infoldings, which are termed fissures and aulei, and these separate the surface into a number of irregular eminences, named convolutions or gyri.