12 1 4 HUMAN ANATOMY. 



also by a lesion in the lateral portion of the occipital lobe, if it extends inwards 

 sufficiently to interrupt the optic radiations. 



In spite of extensive researches the functions of the central ganglia are very 

 little known. 



Lesions of the cerebellar hemispheres may not produce distinct phenomena 

 until the median lobe or vermiform process is involved, when two especially charac- 

 teristic symptoms will almost certainly develop. These are a peculiar disturbance of 

 equilibrium with a staggering gait (cerebellar ataxia), and a troublesome vertigo. 

 Although the patient can scarcely stand alone he may possibly be able to perform 

 the most delicate movements with his upper extremities. The vertigo occurs only 

 in standing or walking, and is then almost always present. Nystagmus is also a 

 frequent symptom. Vomiting is very often present, but is not characteristic, since 

 it is equally frequent in other brain diseases. 



Extending along the floor of the aqueduct of Sylvius and of the fourth ventricle, 

 that is, along the cerebral peduncles, pons and medulla, we find the nuclei of origin 

 of the motor fibres of the cranial nerves. It should be borne in mind that the con- 

 trolling centres of these nerves are in the cerebral cortex. Many automatic centres, 

 as of circulation, respiration, sweating, and regulation of heat, as well as the motor 

 and sensory tracts are found in the medulla. 



Cranio-Cerebral Topography. In order that the surgeon may expose and 

 recognize certain areas of the cortex, it becomes very important that the relations 

 between these areas and the corresponding external surface be well understood. For 

 this purpose advantage is taken of the landmarks of the skull (page 241). From 

 these bony points, ridges and depressions, by means of lines and measurements, the 

 known cortical areas may be accurately mapped out. 



The upper limit of each cerebral hemisphere is indicated, approximately, by the 

 median line at the top of the skull from the glabella to the external occipital protu- 

 berance, due allowance being made for the superior longitudinal sinus, which lies 

 under the skull, in the longitudinal fissure, between the two hemispheres. 



The lower limit is represented by a transverse line, in front, just above the upper 

 margin of the orbit. At the side of the skull the line passes from about a half inch 

 above the external angular process of the frontal bone to just above the external 

 auditory meatus. From here it passes to the external occipital protuberance ; this 

 part of the line corresponding, approximately, to the lateral sinus. The cerebellum 

 lies immediately below this line. 



Of the brain fissures, those of greatest importance in cerebral localization are 

 the Rolandic and Sylvian, since by means of these all the best known cortical centres 

 can be located. Of the two, the fissure of Rolando is much the more important, 

 because the motor, the most definitely known cortical area, is associated with it. Its 

 upper limit is at a point about 12 mm. (one-half inch) behind the mid-point between 

 the glabella and the inion, and about one-half inch from the median line. It passes 

 outward, downward, and forward, approximately, at an angle of 71 with the median 

 sagittal line of the skull. It is 8.5 cm. (3^5 in.) long (Thane), and ends below just 

 above the fissure of Sylvius. Near its lower end it turns rather suddenly downward, 

 so that, in this part, it is not in the line of the angle of 71. 



Many methods have been devised for the purpose of making the line of the 

 fissure on the scalp. 



( '/i ifn< ' . v method consists of folding an ordinary square sheet of paper on the 

 diagonal line, thus dividing an angle of 90 in half, making two of 45. One of these 

 angles of 45 is again halved in a similar manner, making two new angles each of 

 22j/. The paper is then so unfolded that one of the angles of 22 l / 2 is added to that 

 of 45, making a new angle of 67^ ; this will be sufficiently near that of the fissure 

 of Rolando for all practical purposes. 



Horsley s cyrtomctcr consists of two strips, either of thin, flexible metal or of 

 parchment paper, each graduated in inches. The lateral arm is placed at an angle 

 of 67 with the long arm, tin- apex of the angle being at a point 12 mm. or one-half 

 inch behind the mid-point of the long arm. 



Le Fort simply dn-w a line from the beginning of the fissure, above, to the mid- 

 dle of the zygoma, below, and marked off on this line the proper length of the fissure. 



