DISTRIBUTION OF THE OBTURATOR NERVE. 741 the adductor magnus, and the gracilis. In some cases the pectineus is supplied by this nerve or the accessory obturator nerve, but its chief source of supply is undoubtedly from the anterior crural. This fact would seem to indicate that the gracilis muscle, whose supply from the obturator nerve is very constant, should be classed as an adductor muscle, rather than as a flexor, and that this is its true action seems well proven on mechanical principles. Its point of insertion is just below the central point of the limb which it moves, hence, it seizes the limb just beyond the central point, between the fulcrum (the hip joint) and the resistance, and is thus able to greatly assist the adductor muscles. The obturator nerve is thus, physiologically considered, the adductor nerve of the lower extremity, while the muscles which it supplies also act as external rotators of the thigh, on account of the obliquity of their fibers. That the pectineus muscle acts as a flexor as well as an adductor is proven by its nerve supply, as well as by the direction of its fibers and its points of origin and insertion, since it receives filaments both from the anterior crural and obturator. CLINICAL POINTS PERTAINING TO THE OBTURATOR NERVE. The diagnostic value of pain in the region of the knee joint as an evidence of disease in other localities, to which the obturator nerve is either distributed or with which it bears some intimate relations, has been discussed already at some length.' Such a pain may be dependent, however, also upon lesions interfering with the free action of the anterior crural and sciatic nerves, and, for that reason, the course of these three nerves should always be carefully examined before a positive diagnosis can be made as to the exciting cause of pain in the region of the knee. The obturator nerve is even less frequently affected with isolated paralysis than the anterior crural, but, if so, it may be referable to the same list of causes. In addition to the causes mentioned, may be added, however, compression of the See page 734 of this volume. obturator nerve from a strangulated hernia through the obturator foramen, the pressure exerted by the head of a fœtus during its passage through the pelvis, and the use of forceps during difficult labors. From what has been said as to the supply of muscles by this nerve, it is apparent that a patient afflicted with obturator paralysis can not adduct the thigh, or perform the acts of pressing the knees tightly together or of crossing the affected leg over the other. Since the adductor muscles assist in the external rotation of the thigh, this movement is impaired, especially in the sitting posture, when the external rotators attached to the great trochanter are rendered inert. The affected leg soon becomes fatigued in walking, and riding upon horseback is difficult, since the knees can not grasp the saddle. Some disturbances of sensibility may be detected in the regions of the skin supplied by this nerve; these will be the same in character as those mentioned as existing in crural paralysis.' THE ACCESSORY OBTURATOR NERVE. This nerve is sometimes wanting. When it is present, its origin is extremely variable. It may arise from the third and fourth lumbar nerves; from the fourth lumbar and obturator nerves; or by separate filaments derived from the second, third, and fourth lumbar nerves. It descends along the inner side of the psoas muscle, crosses in front of the pubes, passes behind the pectineus muscle, and there divides into branches to the pectineus and the hip joint. It usually gives off a large branch of communication to the obturator nerve (which is often larger than the continuation of the accessory nerve itself), and terminates as a cutaneous nerve to the thigh and leg. The frequent absence of this nerve deprives it of any clinical importance, as it is impossible in any one case to decide if pain in the regions supplied by the obturator nerve is partly due to the accessory obturator or not, while the variations in 1 See page 736 of this volume. THE SACRAL NERVES. 743 the method of origin of the nerve renders it impossible to definitely decide as to the seat of irritation, provided the pain could be traced to the accessory nerve and localized above the pelvis. THE SACRAL NERVES. We now have reached, in the natural progress of this course of lectures, the terminal nerves of the spinal cord. As was the case with those of the lumbar region, the sacral nerves divide into anterior and posterior divisions, but they differ from the lumbar nerves in the fact that these anterior and posterior divisions escape from separate foramina in the sacrum, while, in the portions of the cord above the sacral region, the spinal nerves divide after their escape from the inter-vertebral foramina. These nerves form, by their anterior divisions and the addition of the lumbo-sacral cord, the sacral plexus; while their posterior divisions are distributed to the muscles of the lower lumbar region and to the integument of the gluteal, sacral, and coccygeal regions. The sacral plexus is triangular in shape, and is formed by the lumbo-sacral cord, the three upper sacral nerves (their anterior divisions), and a portion of the fourth sacral nerve. Its constituent fibers converge to form one flattened cord, which leaves the pelvis through the lower part of the great sacro-sciatic foramen, below the pyriformis muscle, while, within the pelvis, the plexus lies upon the pyriformis muscle, and is covered by the pelvic fascia and the two terminal branches of the anterior division of the internal iliac artery (the sciatic and pudic). The branches which are given off by this plexus are arranged, in the table which I now show you, in such a way as to make them apparent to the eye, while the distribution of each is shown in the next table in detail. The first table is not intended to exhibit alone the branches of the sacral plexus, but rather to give the general arrangement of the sacral nerves in their entirety. You will perceive that the arrangement of both the anterior and posterior divisions is considered, and that the component parts of the sacral plexus, as well as its main subdivisions, are clearly set forth. Each of the five branches of the sacral plexus, as well as those included in the muscular group, to which no special names are given, will now be separately described. I have endeavored to embrace in this second table all the points pertaining to the purely anatomical distribution of each of these nerves, but much of interest, from a clinical aspect, still remains in relation to some of them, which can not be shown in a tabular form. This table will, however, prove of assistance to you in reviewing the distribution of the nerve which is, at any time, under discussion, and, furthermore, avoid lengthy descriptions of a purely anatomical character. Taken from the "Essentials of Anatomy " (Darling and Ranney). G. P. Putnam's Sons, New York, 1880. Dorsal nerve of Integument of the dorsum of the penis, penis. THE SUPERIOR GLUTEAL NERVE. This nerve arises from the back part of the lumbo-sacral cord, and, while generally included as a branch of the sacral plexus, can not be, therefore, properly regarded as a nerve of sacral origin. It escapes from the pelvis through the upper part of the great sacro-sciatic foramen, in company with the gluteal vessels, lying above the pyriformis muscle. It divides into a superior and an inferior branch, as is shown in the table' to which I have called your special attention, the former of which accompanies the superior gluteal artery between Modified from a table taken from "The Essentials of Anatomy" (Darling and Ran- ney). |