EOOTS OF THE CEREBRAL NERVES. 385 



7. The facial nerve arises from the outer side of the ante- 



rior end of the corpus trapezoideum, immediately 

 behind the trigeminal nerve. 



8. The auditory nerve is large, and arises from the side 



of the medulla, immediately behind and to the outer 

 side of the facial nerve. 

 9 and 10. The glosso-pharyngeal and pnenmogastric nerves 

 arise close together, by many slender rootlets, from 

 the side of the medulla, close behind, and a little 

 above the root of the auditory nerve. 



11. The spinal accessory nerye arises from the side of the 



medulla and spinal cord by about ten rootlets, the 

 most anterior of which is just behind the pnenmo- 

 gastric, and the hindmost as far back as the fifth 

 spinal nerve. 



12. The hypoglossal nerve arises by a number of rootlets 



from the ventral surface of the medulla, close to the 

 middle line, and to the outer side of the ventral 

 pyramid. 



D. The Structure of the Brain. 



The brain is, from the mode of its formation, tubular ; its 

 cavity being directly continuous with the central canal of the 

 spinal cord. From a very early stage it presents a series of 

 dilatations or vesicles, partially separated from one another 

 by constrictions. Of these vesicles, the first or most anterior 

 one is the fore-brain, or thalamencephalon, from which the 

 cerebral hemispheres arise as hollow outgrowths ; the second 

 vesicle is the mid-brain or mesencephalon ; and the succeeding 

 ones, of which there are at least four or five, are spoken of 

 collectively as the hind-brain. The cavities of the vesicles 

 remain in communication with one another throughout life, 

 and are spoken of in the adult as the ventricles of the 

 brain. 



1. Dissection of the Brain, 

 a. The cerebral hemispheres. 



Lay the brain with its dorsal surface upward, and gently 



CO 



