THE GARDEN TOAD 27 



Examine the brain. In front of the true brain are the 

 olfactory lobes, the nervous centre for the sense of smell. 

 The brain itself is composed of several parts. The anterior 

 portion consists of two elongated parts, the cerebral hemis- 

 pheres; just back of these are the optic lobes or mid brain, 

 consisting of two short lobes, which are followed by the 

 small cerebellum, which in turn is followed by a long part, 

 the medulla oblongata, which runs imperceptibly into the 

 long dorsal nerve, the spinal cord. Note the large optic 

 nerves running out to each eye. How far backward does 

 the spinal cord extend? Note the many pairs of nerves 

 given off from the brain and spinal cord. These nerves 

 branch and subdivide until they end in very fine fibres. 

 Some end in the muscle-fibres, and through them the cen- 

 tral nervous system innervates the muscles. These are 

 motor endings. Still others pass to the- surface and receive 

 impressions from the outside. These last are sensory end- 

 ings. Note that the spinal nerves arise from the spinal cord 

 by two roots, an anterior or ventral, and a posterior or dorsal 

 root. Trace the principal spinal nerves to the body-parts 

 innervated by them. These nerves are numbered as first, 

 second, etc., according to the number of the vertebrae (count- 

 ing from the head backward) from behind which they arise. 



For a more detailed account of the anatomy of the toad 

 (frog) the student may refer to Parker and Haswell's Text- 

 book of Zoology, Vol. II. 



