354 



MORPHOLOGY OF THE CEREBRAL CONVOLUTIONS. 



Fig. 25. 



flV 



at the point s, where these two bases meet, and on the radii s c and s c', two 

 lengths s f and s f, equal to one another and to the radius p" of the third 

 base, then from the points c and c' as centres, and with the lengths c f and c' f ' 



as radii, let us trace two arcs of a circle, their 

 points of intersection on c" will be the centre 

 of the base of the third film, a base which we 

 will then describe with the radius p". Let us 

 in effect suppose the problem solved and this 

 base traced. If we draw from the point n 

 where it terminates in one of the former the 

 right lines n c and n c", which will be respec- 

 tively equal to p and p", these lines will make 

 between them an angle of 60°, like the right lines 

 s c and s c'; whence it follows that the triangle c n 

 c" will be equal to the triangle c s f, in which s c 

 and s f are also respectively equal to p and p", and thus c c" will be equal to c f, for 

 the same reasons the triangle c' v c" will be equal to the triangle c' s f , and conse- 

 quently c' c" will be equal to c' f . Let us propose now 

 to trace the bases of the three partitions. Those of the 

 three films being described, Fig. 25, after the preceding 

 outline we determine as in Fig. 23 the centre d of the 

 partition pertaining to the first two films, and com- 

 mencing from s, by drawing s d making with s c' an 

 angle of 60°, until it meets at d, with the line c c' pro- 

 longed ; we determine likewise the centre f of the par- 

 tition pertaining to the first and the third film by 

 drawing u f, making an angle of 60° with c" u, until it 

 meets at f with c c" prolonged ; finally we determine 

 by the same process the centre g of the third partition. 

 There remains then only to describe from the points d, 

 f and g, as centres, and with the radii d s, f u and g v, 

 arcs of three circles beginning respectively, at the 

 points s, u and v, and directed toward the middle of 

 the figure ; these arcs will be the bases of the three 

 partitions, on the hypothesis, however, that these 

 partitions are portions of spheres. If the figure has 

 been constructed with care, we shall recognize, 1st, 

 that the three arcs just spoken of all terminate at the 

 5 same point o ; 2d, that the three centres, f, d and g 



are disposed in a right line ; 3d, that if we join the 

 point o to these three centres, the angles fod and god are equal and each of 

 60°. 



ps?=~ 



