THE OCULO-MOTOR NERVE 



55 



the dorsum sellge of the sphenoid (Fig. 35). The next part of 

 its course is situated in the lateral wall of the cavernous 

 sinus (p. 115) between the supporting dura mater and the 

 endothelial lining (Fig. 31), where it is closely related to 

 the fourth and sixth nerves. It is here placed lateral to the 

 hypophysis (pituitary body), but is separated from it by the 

 internal carotid artery and the sinus itself. On leaving the 

 anterior end of the cavernous sinus, the oculo-motor nerve 



FIG. 31. Transverse Section through the Cavernous Sinus. 



1. Hypophysis. 



2. Endothelial wall of sinus. 



3. Cavernous sinus. 



4. Internal carotid artery. 



5. Oculo-motor nerve. 



6. Abducent nerve. 



7. Trochlear nerve. 



8. Serous layer of dura mater. 



9. Ophthalmic nerve. 

 10. Sphenoidal air-sinus. 



n. Endo-periosteum of skull. 

 12. Maxillary nerve. 



enters the orbit through the superior orbital (sphenoidal) 

 fissure. 



The Trochlear Nerve has its nucleus in the lower part 

 of the mid-brain. The emerging fibres pass backwards and 

 medially from their origin and, crossing the median plane, 

 leave the posterior surface of the mid-brain immediately 

 below the inferior corpora quadrigemina. The trochlear 

 nerve is exceptional, therefore, in two ways : (i) It arises from 

 the dorsal aspect of the brain-stem, and (2) its fibres decussate 

 after they leave the nucleus, Thereafter, the nerve winds 



