4:00 GENERATION. 



ment of the hemispheres. The middle, or second primitive 

 vesicle, does not undergo division, and is developed into the 

 tubercula quadrigemina, or centres of vision. The posterior, 

 or third primitive vesicle, is divided into two secondary vesi- 

 cles, the anterior of which becomes the cerebellum, and the 

 posterior, which is covered by the anterior, the medulla ob- 

 longata and the pons Yarolii. While this division of the 

 primitive cerebral vesicles is going on, the entire chain of 

 encephalic ganglia becomes curved from behind forward, 



FIG. 43. 



Development of the spinal cord and brain of the human subject. 



A, brain and spinal cord of an embryon of seven weeks, lateral view. 



B, the same, from an embryon farther advanced in development : ft, spinal cord ; <?, enlarge- 

 ment of the spinal cord with its anterior curvature; c, cerebellum; e, tubercula quadri- 

 gemina ; /, optic thalamus ; g. cerebral hemispheres. 



C, brain and spinal cord of an embryon of eleven weeks ; ft, spinal cord ; d , enlargement of the 

 spinal cord, with its anterior curvature ; c, cerebellum; e, tubercula quadrigemina; g, cere- 

 bral hemispheres ; o, optic nerve of the left side. 



C', the same parts in a vertical section in the median line from before backward; ft, membrane 

 of the spinal cord turned backward ; rf, second curvature of the upper portion of tbe spinal 

 cord, which has become thickened and constitutes the peduncles of the cerebrum ; , tuber- 

 cula quadrigemina; /, optic thalami covered by the hemispheres. (LONGET, Traite de 

 physiologie, Paris, 1669, tome iii., p. 892.) 



forming three prominent angles. The first of these angles 

 or prominences (0, Fig. 43, A, B, C), counting from before 

 backward, is formed by a projection of the tubercula quadri- 

 gemina, which, at this time, constitute the most projecting 

 portion of the encephalic mass ; the second prominence (<?, 

 Fig. 43), situated behind the tubercula quadrigemina, is 

 formed by the projection of the cerebellum ; the third (d, 

 Fig. 43, A, B, C), is the bend of the superior portion of the 

 spinal cord. These projections and the early formation of 

 certain parts of the encephalon in the human subject are il- 

 lustrated in Fig. 43, taken from Tiedemann by Longet. 



