=The Optic Thalamus= transmits sensory currents to the cerebral cortex. Lesions in this organ cause sensory paralysis on the opposite side of the body. Afferent currents that do not traverse the thalamus cause reflexes only. It contains one of the roots of the optic nerve and its destruction will impair vision. Its injuries may also produce turning movements. =The Corpus Striatum= transmits motor currents originating in the cerebral cortex. Lesions of its interior (lenticular nucleus) cause motor paralysis and sometimes anæsthesia on the opposite side of the body. Electrical stimulation of this nucleus causes general muscular contractions of the opposite side of the body. Irritation of the surface layers is painless and symptomless. =The Cerebellum= has been long credited with coördination, and Flourens, after its removal from a pigeon, found an utter lack of harmonized movement in walking, springing or balancing. Luciani removed the organ from a bitch and, after full healing of the part, found a lack of muscular tone (a cerebellar ataxy), so that no great muscular effort could be satisfactorily accomplished. After months, marasmus set in and proved fatal. The lack of coördination is especially connected with lesions of the vermiform process, those of the posterior portion causing falling forward and those of the anterior portion, falling backward. Injury to the middle peduncle on one side causes turning or rolling to the opposite side. Under slighter injuries there may be only unsteadiness and staggering like a drunken man. Nausea and vomiting, with more or less stiffness of the neck or oposthotonos, may be present. Rolling of the eyes or squinting may occur. =Focal Cortical Centers of the Cerebrum. Cortical Localization.= Much has been done experimentally and by observation of morbid lesions to locate functions in the different convolutions, and though the subsidiary implication of adjacent and interdependent parts interferes with a perfectly confident diagnosis, yet certain fundamental facts may be borne in mind as contributing to a satisfactory diagnosis. Arloing, on the basis of his own experiments and those of his predecessors, gives the following as applicable to the equine (ass) brain: 1. Stimulation of the origin of the front part of the first frontal convolution, or of the anterior part of the pre-Sylvian convolution, causes approximation of the feet on the opposite side of the body. 2. Stimulation of the superior part of the first frontal convolution or of the superior part of the post-Rolandic convolution causes closure of the jaws and diduction. 3. Stimulation of the anterior end of the upper orbital convolution, or of the anterior part of the pre-Rolandic convolution, leads to movements of the nose and upper lip. 4. Stimulation of the antero-superior part of the lower frontal convolution, or the union of the post-Rolandic with the Sylvian convolution causes movement of tongue and jaws.