SIR CHARLES BELL ON THE THIRD PAIR OF NERVES. 225 



oblongata, a similar junction and decussation takes place between the posterior 

 columns. 



In tracing these columns upwards, we come on ground necessary to our pre- 

 sent inquiry, viz. — the Nodus Cerebri or Pons Varolii. This most conspicuous 

 part of the base of the brain is an intricate mass of fibres, whose commissures and 

 columns interweave, and to what purpose ? Can it be doubted that it is for gene- 

 ral union ? — in order that organs seated apart may be united through the con- 

 nection of their nerves ? 



Below the nodus, the course of the columns is regular ; above it, the course of 

 the corresponding tracts is simple. Here, then, must be seated the mystery, since, 

 but for this intricacy in the nodus, order and simplicity would be displayed 

 throughout the whole nervous system. We are directed in this inquiry by another 

 (•ircumstance. When we consider the nerves of the Encephalon according to the 

 enumeration of Willis (which hitherto has been the acknowledged system), and 

 count them and describe their course, we find six sent to the eye ! The 2d, 3d, 4th, 

 5th, 6th, and 7th, wholly or in part pass into the orbit, into a space not larger 

 than a wallnut shell. It is obvious, that if we discover why these nerves crowd 

 into the orbit, the reason of the variety in the nerves of the base of the brain must 

 also be disclosed to us. 



This consideration points to the organ which has most engaged philosophers 

 of every age and country — the human eye. 



There are many reasons for considering vision as the compound operation of 

 the sense seated in the retina, and the sensibility to the muscular movement of 

 the eyeball. But without entering upon this demonstration, it is sufficient to 

 our present purpose that we observe the surprising power of muscular adjust- 

 ment of the eye in the direction of its axis to the sensation in the retina, or in 

 other words to the object contemplated — as when the attention is directed to the 

 minutest speck, — or the property by which the eye follows objects in motion, the 

 fliffht of a bird or the track of a bombshell. 



Since, then, the relation between the motions of the eyeball and the sense en- 

 joyed by the proper nerve of vision is intimate beyond all comparison, and, I had 

 almost said, comprehension, our first inquiry may take this shape — Ought the 

 motions of the eye, so necessarily conjoined with the proper sense of vision, to be 

 trammelled by the complex relations of the general frame ? — those motions 

 which, from familiarity, appear the simplest possible, but which are in fact the 

 most complex. There is not a muscle in the body, nor a system of muscles, in 

 which combination to a very great extent is not necessary to action. 



The spinal marrow is a system through which the whole body, and especially 

 the four quarters, are combined in action. There is not a limb stretched out 

 without a conforming motion and balancing of the whole body. Walking, 

 running, leaping, swimming, exhibit instances of this combination of the limbs, 



VOL. XIV. PART I. F f 



