Besides the gray matter of the cortex, certain independent masses of gray matter occur in tilt/ cerebellum. These are the corpus dentalum. convoluted body of gray matter situated to the inner side of the centre of the core of white mat ter, and the roof-nuclei of Stilling, situated at the anterior cud of the superior vermiform proc ess and projecting forward into the roof of the ventricle.
The functions of the cerebellum have been made the subject of much discussion and inves tigation. It is itself insensible to irritation, and has been cut away in various animals• without eliciting signs of pain; moreover, its removal or disorganization by disease is generally unaccom panied with loss or disorder of sensibility, ani mals from whom it has been removed being ap parently able to smell, see, hear. and feel as perfectly as before. Flourens extirpated the cere bellum in birds by successive layers. Feebleness and Want of harmony of the movements resulted from the removal of the superficial layers. When he reached the middle layers. the animals became restless; their movements were violent and irregular. By the time that the organ was en tirely renamed, the animals had completely lost the power of flying. walking, standing, and pre serving their equilibrium. When a pigeon in this state was laid upon its back, it could not recover its former position, but fluttered its wings, and saw and tried to avoid a threatened blow. thence volition, sensatbm, and memory were not lost, but merely the faculty of combining the actions of the muscles. From a large series of experiment s of this kind, subsequently made on all classes of animals, Flintrens inferred that the cerebellum belonged neither to the sensitive nor Iu the intellectual apparatus; that it was not the source of voluntary movements, although belong ing to the motor apparatus; that it is the organ for the coOrdination of the voluntary move• meats, or for the excitement of the combined and harmonious action of the muscles.
In spite of the above facts, the extent to which muscular coordination is dependent upon the oerebellnin cannot he considered as satisfactorily determined.
The (47-0)nm—sometimes called the brain proper--constitutes in man the largest part of the eerebro•spinal axis. Lying within the cite its of the skull. its shape conforms to that of the cranial eavity. Anteriorly, superiorly. awl posteriorly. a deep fissure rims lengthwise of the brain, called the great longitudinal fissure, separating the brain into two equal halves or hemispheres. .‘t the bottom of the fissure n. brood Land of fibres—the corpus eallosnm unites the two hemispheres. Flaeh hemisphere presents three surfaces—an outer, which is con vex and corresponds to the hiller surface of the skull; an inner. whieh is lint. lying against the similar surface of the opposite hemisphere, from which it is separated by the falx eerebri; and an under surface, is somewhat concave awl rests upon the anterior and middle foss:e of the skull and upon the Iento•ium cerebelli. The surface of each hemisphere is marked by nu merous elevations and depressions, the former known as convolutions or gyri, the latter as fissures and sulei. These convolutions serve to increase the actual surface of the brain without increasing the actual size of the organ, and the number and extent of the convolutions arc in direct relation to the intellectual development. increasing throughout the ascent of the mammalian scale, and reaching their highest com plexity in civilized man.