THE NECTURUS 61 



oblique on the inner upper border; the retractor bulbi is 

 around the optic nerve and serves to retract the ball. It 

 opposes the levator sheet of muscle under the ball which 

 elevates it slightly. 



Study the eye and note the cornea, the clear layer 

 covering the outer face, the shape of the pupil and iris. 

 Make a median cut through the eye, dividing the eye into 

 a dorsal and ventral half, immerse in water or alcohol and 

 study the following parts. 



The ora serrata is the wavy line that marks the outer 

 limits of the retina. The two chambers of the eye are the 

 space in front of the lens which is called the anterior 

 chamber and the space between the iris and lens which is 

 called the posterior chamber. The retina can be studied 

 only in specially prepared slides. 



Ear 



The ear of Necturus is not difficult for dissection and 

 may be used if desired. 



In a specimen from which the brain has been removed, 

 find the otic capsule and pare down the dorsal side until 

 the cavity is reached. This capsule is largely cartilage and 

 is not difficult to cut away, thus exposing the semicircular 

 canals of the ear. These canals are imbedded in cartilage 

 and bone and must be freed for study. There are three 

 canals an anterior, posterior and horizontal. The lateral 

 or horizontal is more ventral than the other two. The 

 cavity exposed is the vestibule, which is filled with endo- 

 lymph. The whole capsule may be removed and placed 

 in a glass dish for study. 



The three canals are supplied with ampullae where they 

 enter the utriculus. At the anterior end of the ear, the 

 ampullae of the lateral and anterior canals are to be noted. 

 The ampulla of the posterior canal is located at the pos- 

 terior end of the utriculus where the canal enters it. 



