1066 THE NER VE SYSTEM 



punctured for the relief of sciatica. The nerve has also been stretched in cases of locomotor 

 ataxia, the anesthesia of leprosy, etc. In order to define it on the surface, a point is taken at 

 the junction of the middle and lower third of a line stretching from the posterior superior spine 

 of the ilium to the outer part of the tuber ischii, and a line is drawn from this point to the middle 

 of the upper part of the popliteal space. The line must be slightly curved with its convexity 

 outward, and as it passes downward to the lower border of the Gluteus maximus is slightly 

 nearer the tuberosity of the ischium than to the great trochanter, as it crosses a line drawn between 

 these two points. The operation of stretching the sciatic nerve is performed by making an 

 incision over the course of the nerve about the centre of the thigh. The skin, superficial struc- 

 tures, and deep fascia having been divided, the interval between the inner and outer Hamstrings 

 is to be defined, and these muscles respectively pulled inward and outward with retractors. 

 The nerve will be found a little to the inner side of the Biceps. It is to be separated from the 

 surrounding structures, hooked up with the finger, and stretched by steady and continuous trac- 

 tion for two or three minutes. The sciatic nerve may also be stretched by what is known as the 

 "dry" method. The patient is laid on his back, the foot is extended, the leg flexed on the thigh, 

 and the thigh strongly flexed on the abdomen. While the thigh is maintained in this position 

 the leg is forcibly extended to its full extent, and the foot as fully flexed on the leg. This last- 

 named method is uncertain. 



The position of the external popliteal nerve, close behind the tendon of the Biceps on the outer 

 side of the ham, should be remembered in subcutaneous division of the tendon. After it is divided, 

 a cord often rises up close beside it, which might be mistaken for a small undivided portion of the 

 tendon, and the surgeon might be tempted to reintroduce his knife and divide it. This must 

 never be done, as the cord is the external popliteal nerve, which becomes prominent as soon as 

 the tendon is divided. (See also page 527.) 



THE SYMPATHETIC NERVE SYSTEM (SYMPATHICUS) (Fig. 779). 



The distinction of the sympathetic nerve system from the cerebrospinal system 

 is made merely for reasons of convenience. The two systems are intimately 

 connected and the sympathetic is morphologically a derivative of the"central axis 

 disseminated in connection with the nutritive apparatus and establishing relation- 

 ships among the vegetative organs. 



The sympathetic nerve system consists of (1) a series of central ganglia (gan- 

 glia trunci sympathici) connected by a great ganglionic cord, the gangliated cord 

 (truncus sympathicvA], extending from the base of the skull to the coccyx, 

 one gangliated cord on each side of the middle line of the body, ventrolateraii 

 of the vertebral column ; (2) of three great gangliated plexuses (plexus sympathici) or 

 aggregations of nerves and ganglia, situated ventrolaterad of the spine in the thor- 

 acic, abdominal, and pelvic cavities respectively; (3) of smaller or terminal ganglia, 

 situated in relation with the abdominal viscera; 1 and (4} of numerous nerve fibres. 

 These latter are of two kinds communicating, by which the ganglia communicate 

 with each other and with the cerebrospinal nerves; and distributory, supplying the 

 internal viscera and the coats of the bloodvessels. 



Each yangliated cord may be traced upward from the base of the skull into the 

 cranial cavity by an ascending branch, which passes through the carotid canal, 

 forms a plexus on the internal carotid artery and in the cavernous sinus_( Fig. 782), 

 and communicates with certain cranial nerves (p. IQffi); the lower ends of the 

 two cords converge and end in a single ganglion, the ganglion impar (ganglion 

 coccygeum impar], situated ventrad of the coccyx. The ganglia of the cord are 

 distinguished as cervical, thoracic, lumbar, and sacral, and except in the neck they 

 closely correspond in number to the vertebrae against which they lie. They 

 are arranged thus: 



Cervical portion 3 pairs of ganglia. 



Thoracic " 10 to 12 " 



Lumbar " 4 " 



Sacral " 4 or 5 " 



i The ciliary, sphenopalatine, otic, and submaxillary ganglia, already described in connection with the tri- 

 geminal nerve, may be regarded as belonging to the sympathetic system. 



