340 Journal of Comparative Neurology. 



of .55 mm. and an axial diameter of .57 mm. This corres- 

 ponds very closely with the dimensions of the eye of the 

 Europeaii mole at the same age. Kohl gives these diam- 

 eters as about .55 mm. and .61 mm. respectively. 



The shape of the eye is generally that of a sphere, though 

 it may be distorted in many ways. This is very likely due to 

 the action of the hardening solutions. 



From sections through the eye and the entire head one at 

 once sees that the position of the eye is different from most 

 mammals. It is not confined within a bony socket nor in any 

 way protected by a bony frame-work. The nearest it ap- 

 proaches the skull is about .4 mm. That part of the skull to 

 which the extrinsic eye muscles are attached and through 

 which the optic nerve passes is 3. 5- mm. from the eye. It 

 thus lies imbedded in the integument just beneath the skin, 

 quite a distance from the normal position found in most 

 mammals. 



The aqueous chamber is absent and the vitreous chamber 

 is seldom found. The entire space within the sclerotic is filled 

 by the lens and the retina. Occasionally, however, in the 

 region of the optic nerve a small remnant of the vitreous cham- 

 ber still persists. In this respect the common mole differs 

 widely from the description of this stage of the European 

 mole as given by Kohl (4). He finds well developed aqueous 

 and vitreous chambers. 



The eye muscles are present and can be traced back a 

 distance of about 3.5 mm. where they are attached to the 

 skull. 



The optic nerve of the young mole at birth presents some 

 interesting conditions. It can be easily followed along the 

 course of the eye muscles until it penetrates the skull in the 

 neighborhood of the attachment of the muscles. Many of the 

 nerve fibers at this age extend only a short distance beyond 

 their exit from the eye ball. The optic tract, however, can 

 easily be traced because its course is marked by the cells of the 

 optic stalk. These cells are more or less inclosed by the nerve 

 fibers which extend to the brain. As the fibers leave the bulb^ 



