532 



TEXT-BOOK OF PHYSIOLOGY. 



f 



The convergence nucleus, a common nucleus for the conjoint 

 action of the two internal recti muscles. 



4. The superior rectus. 



5. The inferior rectus. 



6. The levator palpebrae. 



7. The inferior oblique. 



Cortical Connections. The 

 oculo-motor nuclei are in histologic 

 and physiologic relation with the 

 motor area of the cerebrum. Nerve- 

 cells in the cortex give off axons 

 which, entering the pyramidal tract, 

 descend through the internal capsule, 

 and the crus cerebri, from which they 

 cross to the opposite side. The end- 

 tufts arborize around the nuclei of 

 the oculo-motor nerve with the ex- 

 ception of the nucleus for the iris 

 sphincter. 



Distribution. After their origin 

 the axons converge to form a com- 

 mon trunk, which emerges from the 

 base of the encephalon, on the inner 

 sideToF the crus cerebri, in front of 

 the pons Varolii. The nerve then 

 passes forward through the sphenoid 

 fissure into the orbit cavity, ' where 

 it divides into a superior and an 

 inferior branch. The former is dis- 

 tributed to the superior rectus and 

 the levator palpebra muscles; the 

 latter is distributed to the internal 

 and inferior recti and inferior oblique 

 muscles (Fig. 244). 



From the inferior branch a short 

 bundle of fibers passes to the ciliary 

 or ophthalmic ganglion, where they 

 terminate, arborizing around the 

 ganglion cells. These fibers are 

 smaller in size than those constitut- 

 ing the bulk of the nerve and belong to the system known as 

 the autonomic. These cells give origin to new axons, the ciliary 

 nerves, "winch enter the eyeball, pass forward between the sclera and 

 chorioid coat, and terminate in the ciliary muscle and iris. Jfee_ 

 ciliary nerves are not portions of the third nerve proper, but penprT" 



FIG. 243. DIAGRAMMATIC VIEW or 

 THE SITUATION AND RELATION 

 OF THE NUCLEI OF ORIGIN OF 

 THE OCULO-MOTOR AND PATH- 

 ETICUS (TROCHLEARIS) NERVES. 

 The oculo-motor nuclei consist 

 of an anterior nucleus, the 

 Edinger-Westphal nucleus (a 

 and b), and a posterior nucleus; 

 the posterior nucleus has a dor- 

 sal, a ventral, and a mesial 

 portion; the decussation of 

 fibers from the dorsal portion 

 of the posterior nucleus is also 

 shown. The. decussation of 

 the fibers of the fourth nerve is 

 also represented. (Edinger.) 



