798 THE NERVOUS SYSTEM. 



Rotation outward of the thigh is impaired from paralysis of the Obturator externus. Some- 

 times there is loss of sensation in the upper half of the inner side of the thigh. 



The great sciatic nerve is liable to be pressed upon by various forms of pelvic tumors, 

 giving rise to pain along its trunk, to which the term sciatica is applied. Tumors growing from 

 the pelvic viscera, or bones, aneurisms of some of the branches of the internal iliac artery, 

 calculus in the bladder when of large size, accumulation of faeces in the rectum, may all cause 

 pressure on the nerve inside the pelvis, and give rise to sciatica. Outside the pelvis exposure to 

 cold, violent movements of the hip-joint, exostoses or other tumors growing from the margin of 

 the sacro-sciatic foramen, may also give rise to the same condition. When paralyzed there is 

 loss of motion in all the muscles below the knee, and loss of sensation in the same situation, 

 except the upper half of the back of the leg, supplied by the small sciatic and the upper half 

 of the inner side of the leg, when the communicating branch of the obturator is large (see 

 page 785). 



The sciatic nerve has been frequently cut down upon and stretched, or has been acupunct- 

 ured for the relief of sciatica. The nerve has also been stretched in cases of locomotor ataxy, 

 the anaesthesia 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 drawn from this 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 Glutens maximus is slightly nearer the 

 tuber ischii than 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 structures, arid deep fascia 

 having been divided, the interval between the inner and outer hamstrings is to be defined, and 

 these muscles 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 traction for two or three minutes. The 

 sciatic nerve may also be stretched by what is known as the "dry" plan. 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. 



The position of the external popliteal, 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. 



THE SYMPATHETIC NERVE. 



The Sympathetic Nervous System consists of (1) a series of ganglia, connected 

 together by intervening cords, extending from the base of the skull to the coccyx, 

 one on each side of the middle line of the body, partly in front and partly on each 

 side of the vertebral column ; (2) of three great gangliated plexuses or aggregations 

 of nerves and ganglia, situated in front of the spine in the thoracic, abdominal, and 

 pelvic cavities respectively ; (3) of smaller ganglia, situated in relation with the 

 abdominal viscera ; and (4) of numerous nerve-fibres. These latter are of two 

 kinds : communicating, by which the ganglia communicate with each other and 

 with the cerebro-spinal nerves ; and distributor?/, supplying the internal viscera 

 and the coats of the blood-vessels. 



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

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

 a plexus on the internal carotid artery, and communicates with the ganglia on the 

 first and second divisions of the fifth nerve. According to some anatomists, the 

 two cords are joined, at their cephalic extremities, by these ascending branches 

 communicating in a small ganglion (the ganglion of Ribes), situated upon the 

 anterior communicating artery. The ganglia of these cords are distinguished as 

 cervical, dorsal, lumbar, and sacral, and except in the neck they correspond pretty 

 nearly in number to the vertebrae against which they lie. They may be thus 

 arranged : 



Cervical portion . . 3 pairs of ganglia. 



Dorsal " . . 12 



Lumbar " . . 4 



Sacral " .4 or 5 



