VIII.] THE COMMON FROG. 113 



of the canal formed from the primitive embryonic 

 groove. 



The nerves generally (which are made up of fibres) 

 proceed forth from the brain and spinal marrow, 

 which latter are therefore called the central, or (from 

 their position along the dorsal axis of the body), the 

 axial portion of the nervous system. 



All the nerves which so proceed together constitute 

 what is called the peripheral, or (because going to the 

 limbs which are appendages of the trunk), the appen- 

 dicidar portion of the nervous system. 



From the brain proceed the nerves of special sense : 

 a pair, one on each side, going to the nostrils (i, the 

 olfactory nerves), another pair going to the eyes (2, 

 the optic nerves), and a third pair going to the ears 

 within the skull (3, the auditory nerves). Other nerves 

 go to the tongue and palate, ministering to taste, and 

 again others to the little muscles (orbital muscles), 

 which move the eyeball in various directions, and to 

 different parts of the face. 



The nerves which come forth from the spinal 

 marrow are called spinal nerves. They proceed out 

 in pairs (one on each side), and are distributed to the 

 limbs and trunk. 



Each nerve consists of fibres, of two sorts pro- 

 ceeding respectively from the ventral (in man an- 

 terior), and the dorsal (in man posterior) aspects of 

 the spinal marrow. But these two kinds of fibres are 

 distributed side by side in the ramifications and dis- 

 tributions of each nerve. 



The fibres which come ultimately from the dorsal 

 aspect of the spinal marrow are those which carry 



I 



