350 Journal of Comparative Neurology. 



present, sometimes omy one is seen, or in some cases neither 

 is found. The aqueous chamber is more uniform in shape than 

 the vitreous. This is no doubt due to the fact that the anterior 

 surface of the lens is generally more uniform than the posterior 

 surface and the cornea is less likely to change its shape than 

 the retina. In this respect the common mole differs widely 

 from the European mole. Kohl describes definite and 

 uniform aqueous and vitreous chambers in Talpa europaea which 

 very closely resemble the condition found in most mammals. 



The extrinsic eye muscles are well developed and can be 

 easily traced back to their insertion near the optic foramen. 



The optic nerve maintains a normal position and at this 

 stage is composed largely of nerve fibres. The nerve is very 

 small and is difficult to follow in a gross dissection. It leaves 

 the eye at quite an angle with the surface (Fig. 19, 23 and 27). 

 It then makes two rather sharp bends which occur within 

 .3 mm. from the eye. The remaining part of its course is 

 almost straight to the optic foramen. The average diameter of 

 the nerve at the lamina cribrosa is .045 mm. It then becomes 

 rapidly enlarged until it reaches a diameter of .135 mm. This 

 enlarged portion extends about .18 mm. from the eye-ball. It 

 then rapidly decreases until it is .0675 mm. in diameter. It 

 maintains this diameter from .41 mm. from the eye to the 

 skull. In the region of the enlarged portion the original cells 

 of the optic stalk, which were described in the young at birth, 

 and the nerve fibers are much more loosely connected and 

 arranged than in the remaining portion of the optic nerve. 

 The increase in diameter of the nerve in this region is also due 

 to the fact that the retinal artery enters it about .2 mm. from 

 the eye and enters the eye along with the fibers. 



In cross sections of the nerve one sees that the cells and 

 nerve fibers are more or less separated into groups or bundles 

 by septa. This condition has been described by Studnicka 

 (14) in Protopterus and many other forms. 



The blood supply to the eye is quite good. The large 

 artery centralis seems out of proportion to the small size of the 

 eye. It has apparently not been reduced in size at the same 



