Charles Russell Bardeen Don 
A study of the development of the peripheral cutaneous nerves leads 
to the belief that some sort of stimulus to growth is exerted upon the 
nerves by areas lacking innervation. In Fig. 5 numerous areas may be 
seen into which nerve branches proceed from several directions. 
Kiihn’s interesting experiments on the regeneration of nerves in the 
dorsal cutaneous region of the frog have an important bearing on the 
mode of forward growth of nerves. When an area of the skin was de- 
prived of its nerve supply by cutting two or three main nerve-trunks dis- 
tributing branches to it, he found that from nerves in the neighboring 
regions new nerve-fibres extended into the deprived area. In this inner- 
T 
Fic. 5. <A portion of the nerve-plexus formed by the lateral cutaneous branches 
of the dorsal divisions of two thoracic nerves of a pig embryo 4 cm. long. Tr. Main 
trunk of each nerve. 38 diam. 
vation new nerve-paths and peripheral plexuses not corresponding with 
the old were often formed, or the growth of the new fibres showed no 
regular order. This last was especially true of nerve-fibres arising from 
the central ends of the cut nerves. 
During embryonic development nerve-fibres derived from very differ- 
ent sources and destined for a different ultimate distribution often take 
common paths for a part of their course. Good examples of this may 
be seen in the distribution of the vaso-motor nerves and in the relations 
entered into between the trigeminal nerve, the facial nerve and the cervi- 
cal nerves. Popowsky has called attention to the development of anas- 
tomoses between the fifth and seventh cranial nerves. 
A given cutaneous area with the nerves distributed to it may during 
