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TEXT-BOOK OF PHYSIOLOGY 



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 



cortex give off axons which, entering the 

 pyramidal tract, descend through the inter- 

 nal 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 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 enceph- 

 alon, 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 distributed to the superior rectus 

 and the levator palpebra muscles; the lattei 

 is distributed to the internal and inferior 

 recti and inferior oblique muscle (Fig. 267), 

 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 forward between 

 the sclera and chorioid coat, and terminate 

 in the ciliary muscle and the sphincter oi 

 the pupil. The ciliary nerves are not por- 

 tions of the third nerve proper, but periph- 

 eral sympathetic neurons. As the ciliary 

 ganglion receives filaments from the caver- 

 nous plexus of the sympathetic and fila- 

 ments which become a part of the trigeminal nerve, it is probable that the 

 ciliary nerves contain not only motor, but vaso-motor and sensor fibers 

 as well. 



Properties. Stimulation of the nerve near its exit from the encepha- 

 lon is followed by contraction of the muscles to which it is distributed 

 with the following results, viz. : 

 i. Diminution in the size of the pupil. 



FIG. 266. DIAGRAMMATIC VIEW OF 

 THE SITUATION AND RELATION OF 

 THE NUCLEI OF ORIGIN OF THE 

 OCULO-MOTOR AND PATHETICUS 

 (TROCHLEARIS) NERVES. The oculo- 

 motor nuclei consist of an anterior 

 nucleus, the Edinger-Westphal nucleus 

 (a and &), and a posterior nucleus; 

 the posterior nucleus has a dorsal, a 

 ventral, and a mesial portion; the de- 

 cussation 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.) 



