62 THE NECTURUS 



The vestibule is divided into two parts, the utriculus 

 and sacculus. The utriculus is the dorsal sac, into which 

 the canals enter. The sacculus is the ventral sac. The 

 sacculus is very shallow and indistinct and contains the 

 otolith or ear stone. When the ear is removed from the 

 head this stone can be seen in position if the light is 

 directed through it from below. 



Drawing 22. Make an enlarged drawing of the otolith. 



The auditory or the eighth cranial nerve supplies the 

 parts of the ear. Before the capsule is removed for study 

 note the auditory nerve where it comes through the skull 

 and branches to supply the vestibule and canals. In de- 

 calcified specimens the nerves are easily seen and can be 

 followed to the ampullae, utriculus and sacculus. 



If desired, some specimens may be cleared in one of the 

 clearing agents to make the nerves more distinct. The ear 

 has no external meatus but ends blindly. The stapes and 

 columella extend out from the fenestra vestibular and 

 articulate with a projection on the squamosal. It is prob- 

 able that the most important function of the ear in the 

 Urodeles is equilibrium, with the detection of sound as a 

 secondary function. 



BRAIN 



After soaking the skull in nitric acid (10%) for two or 

 three days, the bones become soft and are easily cut away 

 thus exposing the brain on the dorsal side. First remove 

 most of the muscles and then with a sharp scalpel shave 

 away the dorsal surface of the skull until the brain cavity 

 is reached. Complete the exposure until all of the brain 

 is visible. The cranial nerves are plainly seen and need 

 little further dissection to show the roots. To show the 

 course of the nerves and their termination, more careful 

 dissection will be needed. Note the pigmented pia mater 

 covering the brain. Place a piece of the pia mater on a slide 



