THE ENCEPHALIC OR CRANIAL NERVES 631 



3. 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 



FIG. 263. DIAGRAM SHOWING THE NUCLEI OF ORIGIN OF THE MOTOR OCULI NERVES AND 

 THEIR RELATED OCULAR MUSCLES, i. The sphincter pupillae nucleus; 2. The ciliary muscle 

 nucleus; the fibers of these nuclei arborize around x, the ciliary ganglion from which axons, 

 the ciliary nerves pass into the eyeball to be distributed to the iris and ciliary muscle; 3,3'. 

 The internal rectus nucleus and muscle; 4,4'. The superior rectus nucleus and muscle; 

 5,5'. The inferior rectus nucleus and muscle; 6,6'. The inferior oblique nucleus and muscle; 

 7,7'. The levator palpebral nucleus and muscle. 



cortex give off axons which, entering the pyramidal tract, descend through 

 the internal capsule, and the cms cerebri, from which they cross to the 

 opposite side. The end-tufts arborize around the nuclei of the oculo- 

 motor nerve with the exception of the nucleus for the iris sphincter. 



Distribution. After their origin the axons converge to form a 

 common trunk, which emerges from the base of the encephalon, on the 

 inner side of 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 * nd inferior oblique muscle 

 (Fig. 263). 



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 constituting the bulk of 

 the nerve and belong to the system known as the autonomic. These cells 

 give origin to new axons, the ciliary nerves, which enter the eyeball, pass 



