THE CRANIAL NERVES. 543 



and parallel. The image of the paralyzed eye lies external to that 

 of the normal eye. 



Function. The function of this nerve is to transmit nerve im- 

 pulses to the external rectus muscle and excite it to contraction. 



SEVENTH PAIR. THE FACIAL. 



The seventh cranial nerve, the facial, consists of peripherally 

 coursing nerve-fibers, which serve to bring the nerve-cells from 

 which they arise into relation with most of the superficial muscles of 

 the head and face. 



The muscles supplied by this nerve, as stated by the general 

 anatomists, are as follows : The occipito-f rontalis, corrugator super- 

 cilii, orbicularis j)alpebrarum, levator Jabii superioris, afequgjnasi, 

 zygomatici, the pyramidalisjiasi, the compressor_nasi, the depressor 

 alae nasi, levator anguli oris, buccinator, orbicularis oris, depressor 

 angulijpris, depressor labii inferioris, the levator menti, the posterior 

 belly of the digastric, the stylo-hyoid, and the platysma myoides. 



Origin. The nerve-fibers or axons composing the seventh nerve 

 arise for the most part from a jiucleus of large multipolar nerve-cells 

 situated about five millimeters beneath the upper half of the floor 

 of the fourth ventricle toward the middle line. 



From this nucleus, which is about four millimeters long, axons 

 emerge which at first pass inward and backward as far as the epen- 

 dyma of the ventricle ; they then turn on themselves, forming an arch 

 that encloses the nucleus of the sixth nerve; they then course down- 

 ward and outward, emerging from the pons at its lower border between 

 the olivary and restiform bodies. As the axons approach the floor 

 of the ventricle collateral branches are given off which, crossing the 

 median line, arborize around the nerve-cells of the opposite facial 

 nucleus. 



Clinical observations and histologic investigations also render it 

 probable that the fibers distributed to the occipito-frontalis, the cor- 

 rugator supercilii, and the upper half of the orbicularis palpebrarum, 

 are derived from the oculo-motor nucleus, and, descending the 

 posterior longitudinal bundle, enter the trunk of the facial as it 

 turns to pass forward through the pons. It is also probable, for 

 similar reasons, that the fibers distributed to the orbicularis oris are 

 derived from the hypoglossal nucleus. 



Cortical Connections. The nucleus of the facial nerve is in 

 histologic and physiologic connection with the facial region of the 

 general motor area of the cerebral cortex. From the cells of this 

 region axons descend through the pyramidal tract, the internal cap- 

 sule, and the crus cerebri, beyond which they cross to the opposite 

 side and arborize around the cells of the nucleus already described. 



