240 SIR CHARLES BELL ON THE FOURTH AND SIXTH 



crosses all the other nerves, and, though crowdmg with them into the orbit, forms 

 no relation Avith them, but is altogether given to the abductor muscle.* 



Again, in following the root of the facialis, and especially that portion of it 

 which arises from the respu-atory tract, we find a relation established between it 

 and the root of the fourth nerve or trochlearis ; and this delicate nerve passes for- 

 ward like the other, enters the /o:''amen lacerum, and gains the bottom of the or- 

 bit, touches no other nerv^e, but is wholly given to the STiperior oblique muscle. 



If an objection should be made to the circuitous course of these nerves, as 

 the source of the relations between the muscles, how else are the sympathies to 

 be accounted for ? and what interpretation are we to put upon the fact, that 

 wherever there are 7'ecti and oUiqui muscles of the eye, — wherever the eye pos- 

 sesses protecting motions, we find the same arrangement of the third, fourth, and 

 sixth nerves, from man downwards. f 



Surely it is time to read off the anatomy of the nervous system, — to seek for 

 the relations of parts tlirough theu* nerves, — to ask om'selves why there are such 

 deviations in their course, — and why these deviations are constant, not in indivi- 

 duals only, but in the different classes of animals ? If, with this view, we ask 

 ourselves Avhy the facial nerve takes a course different from the fifth, the func- 

 tions of the part to which it is distributed do sufficiently inform us, that the fea- 

 tures must be joined in sympathy or unison with the act of respiration. If we 

 inquh-e why its branches reach to the eyelids, to the very part through which 

 the branches of the fifth pass, we have only to notice the necessity for a guarding 

 action of the eyelids in all excited conditions of the respiratory system. I need 

 not here repeat my former observations. 



In the same manner we may interpret the course of the spinal accessory 

 nerve, or the reverted course of the recurrent of the par vagiim. 



In looking generallj^ to the remarkable deviations in the course of the nen^es, 

 we shall find that they are confined to those which join distant parts in the act 

 of breathing, or modify the act of breathing, as in speaking, swallowing, &:c. No 

 such irregularities are found in the system of nerves wliich minister to voluntary 

 motion and sensation. They are distributed with a perfect symmetry or regu- 

 larity. 



And in the orbit, if we take away the respu*atory of the face (the facialis), 

 and the nerves resulting from that connection, viz. the fourth and sixth, the in- 

 tricacy of the orbitary nerves is removed ; there would remain one for vision, 

 another for common sensibility, and a third for motion. 



* Where there is a retractor muscle, this abducens nerve supplies it, which strengthens the sup- 

 position of a relation between the retraction of the eye and its simultaneous direction inwards. 



I Taking tlie factd of the anatomy into account, and the actions of these muscles, the subject be- 

 comes of great interest, as connected with the expression in the eye. 



