18 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



Similarly with the skin, the median nerve-trunk 

 supplies a patch of the palm that has obviously functional 

 unity, but 1st thoracic nerve-root supplies such incon- 

 gruities as the front of the little finger and of half the 

 ring finger, together with the tip of the point of the 

 •elbow. 



It is the formation of functional collections of nerve- 

 fibres (peripheral nerve- trunks) out of morphological 

 collections (nerve-roots) which is the meaning of the 

 interlacements of adjacent spinal segmental nerves in the 

 limb plexuses. The reply to the frequently asked question 

 as to the explanation of the distribution of the spinal 

 nerves of the brachial and pelvic limbs by plexuses, while 

 the spinal nerves of the trunk region are not distributed 

 hy plexuses, is in my opinion as follows. In the trunk 

 region the innervation of the muscles of the skin is, as 

 regards the distribution in them of the segmental nerves, 

 •a system of comparatively slight overlap : the peripheral 

 territory of each segmental nerve — especially each motor 

 territory — is confluent with, but does not mingle nearly 

 so widely with the neighbour territories as in the limb 

 regions. That is, in other words, each several area 

 of skin and of muscle, especially of the latter, has in 

 'either of the limbs a more pluri-segmental spinal innerva- 

 tion than a comparable area in the trunk. The anatomical 

 mode of innervating a definite area of tissue is, as we know, 

 by means of collecting the nerve-fibres for the region into 

 a nerve-trunk ; where the innervation is pluri-segmental 

 the nerve-trunk will naturally be combined from 

 components of several segmental nerves — where several 

 such areas co-exist several pluri-segmental nerve-trunks 

 will be formed and the separate segmental nerves will be 

 split up into components, which become redistributed in 

 the combinations which constitute the pluri-segmental 



