AMPHIBIA. 51 



FIG. II. 

 VENTEAL ASPECT. 



THIS figure, and the second in the next plate, exhibit the base of the brain, and 

 the anterior surface of the spinal cord. 



a. Commissure of the optic nerves, and the connection with the part in the situa- 

 tion of the mammillary eminences. The pituitary gland has been removed. 



The base of the brain is very smooth, and covered with a thick pia mater ; so that 

 the separation at the usual places of the several eminences is not distinctly observed 

 before this is removed. 



The anterior bundles of the nerves of the cervical portion of the spinal cord are 

 much larger than the posterior ; those of the thoracic much smaller ; and those of the 

 sacral rather larger. The first two cervical nerves are formed entirely of filaments 

 from the anterior surface ; the anterior trunk of the first gives filaments to the cervical 

 muscles, and joins a branch of the ninth, and then gives filaments to the outside of the 

 carotid artery, and terminates in the sterno-thyroid muscle, and one attached to the 

 back of the ossophagus ; the posterior trunk communicates with the posterior branch of 

 the ninth, and terminates entirely in the muscles at the back of the neck ; the anterior 

 trunk of the second passes to a long muscle on the anterior part of the neck, and the 

 posterior to others on the posterior. Sometimes only the first cervical nerve is formed 

 entirely from filaments of the anterior surface of the spinal cord, and then the second 

 has a filament from the posterior surface, and gives the branch to the skin of the face, 

 instead of the third. A branch from the third cervical nerve may be traced through a 

 portion of muscle to the skin of the face, and one from each of those below it to the 

 skin of the neck. 



H 2 



