174 SOMATIC AND SPLANCHNIC NERVES. [BOOK i. 



this system splanchnic fibres from the central nervous system are 

 distributed to the tissues of the viscera, some of them on their 

 way passing through secondary ganglia o-, and, it may be, tertiary 

 ganglia. There are however, as we shall see, certain nerves or 

 fibres which do not run in the sympathetic system, and yet are 

 distributed to the viscera and are ' splanchnic ' in nature. We 

 cannot therefore use the word sympathetic to denote all the 

 fibres which are splanchnic in nature. On the other hand the 

 'splanchnic nerves' of the anatomist form a part only of the 

 splanchnic system in the above sense, the term thus used is 

 limited to particular nerves of the splanchnic system distributed 

 to the abdomen ; and the double use of the term splanchnic might 

 lead to confusion. The difficulty may perhaps be avoided by calling 

 the splanchnic nerves of the anatomist " abdominal splanchnic." 

 The majority of these splanchnic fibres seem to be efferent in 

 nature, carrying impulses from the central nervous system to the 

 tissues, some ending in plain muscular fibres (m) others in other 

 ways (#); but some of the fibres are afferent (s) and convey 

 impulses from the viscera to the central nervous system, and it is 

 possible that some of these begin or end in epithelial cells of the 

 viscera. 



We shall have occasion in the next chapter to speak of nerves 

 which govern the blood vessels of the body, the so-called vaso- 

 motor nerves. A certain class of these, namely the vaso-constrictor 

 nerves or fibres are branches of the splanchnic division of the 

 cerebrospinal nerves, and as we shall see the vaso-constrictor 

 nerves of the skeletal muscles, skin, and other parts supplied by 

 somatic nerves, after running for some distance in the splanchnic 

 division (F), turn back (r. v) and join the somatic division, the 

 fibres of which they accompany (v. m) on their way to the tissues 

 whose blood vessels (m') they supply ; some of these fibres however 

 run not peripherally towards the skin but centrally towards the 

 spinal cord and probably supply the membranes of the cord. 

 Where the communicating branch from the spinal nerve to 

 the sympathetic ganglia consists of two parts, the white ramus 

 communicans and the grey ramus communicans, these revehent, 

 backward turning splanchnic fibres run in the grey ramus; 

 but in the case of some of the spinal nerves it is not possible 

 to distinguish a grey ramus as separate from a white ramus. 

 Besides these vaso-constrictor fibres, other fibres of different 

 function, of which we shall have to speak later on, run from 

 the spinal nerves into the splanchnic system and then back again 

 to the somatic system. 



We have seen ( 68) that a nerve going to a muscle is 

 composed of nerve fibres, chiefly medullated, some however being 

 non-medullated, bound together by connective tissue. The same 

 description holds good for the whole somatic division of each of 

 the spinal nerves. The splanchnic division also consists of me- 



