NERVES OF MAMMALIA. 



149 



In some Marsupials the optic nerve grooves the orbito-sphenoid, 

 escaping by a cleft continuous with the fissura lacera anterior 1 : 

 in higher Mammals the nerve escapes by a special 'foramen 

 opticum.' The extra-cranial parts of the nerves are remarkably 

 long in Whales, 2 and in all Cetacea they diverge from the chiasma 



128 



Base of human brain, with origins of nerves ; half natural size. 



at a wide angle, fig. 60, 2, 2. This becomes less open as the 

 Mammals rise to Man, fig. 128, b. 



The oculo-motor or 'third' nerve, fig. 60, 3; fig. 128, c 9 and 



1 xliv. pp. 323, 329. 2 xciv. p. 387. 



