THE NERVOUS SYSTEM 



91 



canal. Grey nerve-matter contains nerve-cells, 

 the largest of which are found in the ventral 

 part of the mass and give origin to motor nerve- 

 fibres. 



The Brain (Fig. 49). — In accordance with its 



XI M 



X iX 



c\m 



m 



Fig. 49. — Brain seen from the Side. 



cb., cerebral hemisphere ; o.l., optic lobe ; cbl., cerebellum ; m., medulla 

 oblongata ; I., olfactory lobe ; II. to XII., 2nd to 12th cerebral nerves. 



development from three hollow dilatations of 

 the embryonic nem-al tube (see p. 130), the 

 brain may be divided into three main parts — 

 the hind -brain, the mid-brain, and the fore- 

 brain. The original cavities of the embryonic 

 vesicles are represented by the ventricles and 

 the aqueduct, which are continuous with the 

 central canal of the spinal cord. 



