CH. VIII] FROGS, TOADS, AND NEWTS 271 



circumstances. If the hemispheres are removed the frog 

 still swims when put in water, crawls so as to rest on 

 a horizontal surface, avoids obstacles in its path, swallows 

 and breathes. Bat none of these actions are performed 

 except the appropriate stimulus be applied, and on the 

 other hand any given stimulus is followed with mechanical 

 certainty by the appropriate action. The hemispheres 

 then are the seat of the will ; the other portions of the 

 brain are concerned with the receipt of impulses from 

 without, and with the co-ordination of muscular actions. 

 The spinal cord of itself, after severance from the brain, 

 is able to carry out many complex reflex actions and these 

 often of a purposeful character : in life it is also the main 

 road of communication between the brain and the spinal 

 nerves which are distributed throughout the body. From 

 the brain there are given off ten pairs of cranial nerves 

 which pass through the walls of the cranium to their 

 several destinations. The subjoined table (p. 2*73) shows 

 their names and functions. 



The spinal cord gives off also ten pairs of nerves which 

 pass out between the successive vertebrae. Each arises 

 by two roots, a dorsal and a ventral, which unite to form 

 one nerve. The dorsal root bears upon it a ganglionic 

 enlargement, and is composed of nerve fibres conveying 

 sensory impulses only ; the ventral root on the other hand 

 contains only motor fibres. Conspicuous upon the spinal 

 ganglia are white calcareous patches the periganglionic 

 glands or calcareous sacs. Lenhoss^k 1 states that there 

 are usually two to each ganglion, covering its sides and 



1 Arch. f. mikrosk. Anat. xxvi. 



