2IO Journal of Comparative Neurology. 



into its terminal divisions, the fibers of the posterior element 

 occupy the ventral part of the nerve. As the nerve approaches 

 the nasal capsule, the anterior element separates into three 

 divisions ; one of these turns laterad and terminates in the most 

 posterior portion of the olfactory epithelium, while the other 

 two continue cephalad and innervate the anterior olfactory 

 areas. The posterior element of the nerve, however, turns 

 abruptly laterad from the point of division in the nerve and 

 passes anteriorly of the internal nares, across the ventral sur- 

 face of the olfactory epithelium, and terminates by two 

 divisions in Jacobson's organ. 



It is possible that some fibers of the posterior element 

 of the olfactory nerve pass over into the anterior element during 

 their close contact with it and through this course terminate in 

 the olfactory epithelium proper, but there is no direct evidence 

 of such a condition. On the other hand, comparative evidence 

 indicates that the two elements are morphologically distinct. 



II. The Optic Nerve. 



The optic nerve passes cephalo-laterad from the chiasma 

 to its foramen in the lateral wall of the cranium. Beyond this 

 it inclines a little cephalad and passes ventrally of the r. 

 ophthalmicus profundus V, dorsally of the m. rectus internus, 

 and into the antero-mesial side of the m. retractor bulbi. The 

 latter muscle is inserted about the entrance of the optic nerve 

 into the eye. 



III. The Eye-Muscle Nerves. 



I. — TJte Oculomotorius. 



The foramen of the third nerve is in the lateral wall of the 

 cranium only a short distance posteriorly of the optic foramen. 

 Outside the cranial cavity the relations of the oculomotorius 

 vary greatly. Indeed, the variation is such that it is impossi- 

 ble to describe the nerve of any one specimen as typical. For 

 this reason, and also because some of the variations I have 

 observed are important in interpreting some otherwise obscure 

 points, I give an account of several specimens with more or 



