578 TEXT-BOOK OF PHYSIOLOGY 



of the cerebrum in the pigeon completely abolishes intelligence anc 

 destroys the capability of performing volitional movements. Th( 

 pigeon remains in a state of profound stupor, though retaining the cap 

 ability of executing reflex or instinctive movements. It can temporarily, 

 be aroused by loud noises, light placed before the eyes, pinching of th< 

 toes, etc., but it soon relapses into a condition of quietude. Coinciden 

 with the destruction of the cerebrum there occurs a loss of memory 

 reason, and judgment, and the animal fails to associate the impression 

 with any previous train of ideas. The higher the animal in the scale o 

 development, the more striking is the loss of mentality after remova 

 of the cerebrum. 



4. Experimental interference with the blood-supply to the cerebrum is followec 

 by a diminished or complete cessation of its activities. There is per 

 haps no organ of the body that is so directly dependent upon its blood 

 supply for the continuance of its activities as the cerebrum. Thi 

 supply of blood is furnished by four large blood-vessels: viz., the twc 

 carotid and the two vertebral arteries. These vessels, after entering 

 the cavity of the skull, give off branches which unite to form the "circl< 

 of Willis." From this circle, large branches are given off which ente: 

 the cerebrum and distribute blood to all its parts. After passing througl 

 -v the capillaries the blood, greatly altered in chemic composition, ii 

 returned by large veins. The large volume of blood that is present ii 

 the brain and the marked changes in composition that it undergoes whil< 

 passing through the brain indicate a very active and complex metab 

 olism in this organ. By means of the anatomic arrangement of th< 

 blood-vessels at the base of the brain, the blood-supply is equalized 

 It also explains why, when one, or even two, of the four large vessel; 

 are occluded by pathologic deposits or surgical procedures, brail 

 activity continues, though perhaps diminished in degree. Occlusior 

 of all' four vessels, however, is at once followed by a complete abolitior 

 of all forms of cerebral activity. An experiment performed by Brown 

 S6quard illustrates the dependence of cerebral activity on the blood 

 supply. A dog was beheaded at the junction of the neck and chest 

 After a period of ten minutes all evidences of life had entirely ceased 

 Four tubes connected with a reservoir of warm defibrinated blooc 

 were then connected with the four arteries of the head. By means of i 

 pumping apparatus imitating the action of the heart the blood wai 

 driven into and through the brain. After a few minutes cerebral activ 

 ity returned, as shown by contractions of the muscles of the face anc 

 eyes. The character of the contractions were such as to convey tht 

 idea that they were directed by the will. These vital manifestations 

 continued for a period of fifteen minutes, when on the cessation of tht 

 artificial circulation they disappeared, and the head exhibited once 

 more the usual phenomena observed in dying: viz., contraction anc 

 then dilatation of the pupils and convulsive movements of the muscles 

 of the face. , 



The Localization of Functions in the Cerebrum. By the term 

 localization of functions, is meant the assignment of definite physiologit 

 functions to definite anatomic areas of the cerebral cortex. From experi 

 ments made on the brains of animals, by the observation and association o 



