LESSON 86.1 NERVOUS SYSTEM IN MAMMALIA AND MAN. 279 



1257. This is represented to some extent, in three views of the 

 human brain from an Embryo (Figs. 393, 394, and 395). The first 

 (Fig. 393) is seen from behind ; a, the optic lobes, or, as they are 

 called, from their four-lobed character in the human subject, corpora 

 quadrigemini ; b, the cerebral hemispheres ; d, cerebellum ; *, me- 

 dulla oblongata. 



1258. The second (Fig. 394) and the third (Fig. 395) have the 

 same letters of reference down to e ; the second is a side, and the 

 third a sectional (perpendicular) view ; g, the floor of the third ven- 

 tricle ; i, olfactory nerve ; /, optic thalamus. 



1259. We see here a chain of resemblances corresponding with 

 the progressive development observed in the lower animals ; the 



FIG. 393. Fia. 394. FIG. 395. 



Brain of human Embryo, Side view. Sectional view. 



from behind. 



human brain passes through the phases of improving development, 

 which distinguishes the highest from the lower creatures ; and we 

 are naturally led to the same conclusion with regard to the archi- 

 tecture of the human brain, that we are led to establish as the 

 principle of development in the inferior creatures that it is com- 

 posed of primitive chords, primitive ganglia upon those chords, 

 commissures to connect the ganglia, and developments from those 

 ganglia. 



The human brain, therefore, may be supposed to consist of a 

 number of elements, which are more or less diffused amongst the 

 lower animals, and which in them constitute the several ganglionic 

 masses that we find them to possess. 



The more widely these elements are diffused, and the more fre- 

 quent the repetition of these little brains, the lower the individual in 

 the scale' of being. 



Thus, the Nereis nuntia, with its 1,000 ganglions, is lower than 

 a Caterpillar ; which is, in its turn, lower than the perfect Insect ; 

 for in the latter we find a greater concentration of the Cerebrum, to 

 supply an increased number of organs of special sense, all of which 

 have attained a higher, a more refined development. 



The organs of locomotion in the perfect insect have also become 



