THE MUSCULAB SYSTEM. 263 



terminal plexus consists only of extremely minute fibrils, mea- 

 suring 000' 1 — 0-0025'" in diameter. In some cases even, the 

 gradual attenuation of the fibres may be directly observed, 

 proving that the diminution in size does not take place, in 

 this case at least, in consequence of division. Thus, in the 

 omohyoid, I have noticed several nerve-fibres of 0001 — 

 0-0053 '", derived from trunks measuring 005 — 0'07'", become 

 attenuated, within a distance of 0*15 — 02'", to a diameter of 

 0-002 — 00026"', and after a further course of 0-4—0-5'", 

 acquire that of the smallest fibrils, or 0-001'". Simultaneously 

 with this change in size, the nerve-fibres assumed in all 

 respects the aspect of the so-termed sympathetic nerves, and 

 ultimately became pale, with a simple contour line, and dis- 

 posed to form varicosities; at the same time, that they 

 appeared to lose every vestige of a coat composed of con- 

 nective tissue, they still retained dark borders, and consequently 

 were not non-medullated fibres (or free axis-cylinders), such 

 as are seen in other terminations of nerves. 



Nervi vasorum (vascular nerves), accompanying the bundles 

 of vessels, occur in all muscles, and, according to the size of 

 the latter, form larger or smaller branches. They are com- 

 posed only of the smallest fibres, and always follow the course 

 of the large vessels, which can still be recognised as arteries 

 and veins. I have not seen how they terminate — and this 

 much only I know — that they are never met with on the 

 capillaries, and very frequently, also, are not to be found, on 

 the smallest arteries and veins. Occasionallv, one or more 

 fibrils from the terminal plexus of the muscular nerves may be 

 seen to join these vessels ; a circumstance quite in accordance 

 with the demonstrable fact, that the vascular nerves in many 

 parts, for instance in the extremities, are derived from the 

 spinal nerves. 



The smaller tendons contain no nerves, and the larger, such 

 as the tendo Achillis and the tendon of the quadriceps femoris, 

 only vascular nerves. The fascia and sheaths of tendons are 

 also without nerves, as well as the synovial capsules of the 

 muscular system, so far as I am at present aware. 



Lin many of the small muscles, the extent of space included 

 in the distribution of the nerve is extremely limited, as for 



