RELATION BETWEEN STRUCTURE AND FUNCTION. 6 



considered sufficient to connect the two. The arm and 

 hand offer a good field for an attempt to institute an 

 enquiry into the connection between the two. I will, 

 therefore, ask you to follow a brief sketch of the 

 morphological structure, and some remarks upon their 

 function ; and that done, each can enquire of himself to 

 what measure the morphological structure has helped 

 toward the understanding of the problems of the perform- 

 ance of the function. 



If you look at this outline of the human body you will 

 note that in the chest and trunk at least, there is quite 

 evidently a segmental arrangement of the body's structure. 

 If you turn to this picture of the spinal cord lying in the 

 canal of the vertebrae, its composition out of a fore-and-aft 

 series of segments is still more obvious. The segments 

 or metameres of the body appear to possess one spinal 

 nerve apiece. If now we turn to this photograph of the 

 nerves passing from the spinal cord into the limb, we see 

 that a short series of these spinal segmental nerves all go 

 into it. This suggests that the limb is like the trunk 

 composed of metameres essentially arranged segmen- 

 tally, and built up as is the rest of the body. But there is a 

 difficulty in deciding what part of the limb is constituted by 

 this or by that segment. The segmental nerves that issue 

 from the spinal cord into the limb commingle together 

 in a network or plexus. The brachial plexus, which is 

 before you in the photograph, is compounded of five, 

 sometimes of six spinal nerves. The nerve-trunks that 

 issue from it to the muscles and other structures of the 

 limb have obtained their nerve-fibres from various of the 

 spinal nerves, and each of them from several. To unravel 

 by gross anatomy, this intricate plexus is impossible. 

 Professor Krause, the anatomist of Berlin, has further 

 pointed out that not only was he unable to unravel 



