1352 



HUMAN ANATOMY. 



THE COCCYGEAL PLEXUS. 



6. The sacro-coccygeal nerves (nn. anococcygei) are derived from a small 

 nerve inosculation called the coccygeal plexus (plexus coccygeus), a structure formed 

 by the fifth sacral and the coccygeal nerve, with a contribution from the fourth sacral 

 which descends over or through the great sacro-sciatic ligament. The fifth sacral, 

 having been joined by this twig from the fourth, descends along the margin of the 

 coccyx and is joined by the coccygeal nerve, the resulting nerve-bundle constituting 

 the coccygeal plexus. From it arise minute filaments which pierce the great sacro- 

 sciatic ligament and are distributed to the integument in the immediate neighbor- 

 hood of the coccyx (Fig. 1084). 



Practical Considerations. Of the branches of the sacral plexus, the great 

 sciatic nerve is the most important, owing to its size, its extensive distribution and 

 its exposed position. The greater part of the sacral plexus is continued into the 



FIG. 1128. 



Clans clitoridis 



Deep layer of 

 triangular ligament 



Dorsal nerve of clitoris 

 Superficial perineal 



Bulbo-cavernosus 



Ischio- cavern OS us 



Inferior pudenda) nerve 



Posterior superficial 



perineal nerve 



Anterior superficial 



perineal nerve 



Transversus perinei 



superficial 



Perineal division of 

 pudic nerve 



Inferior hemorrhoidal 



nerve 



Sphincter ani 



Anal fascia 



Deep fascia of buttock 



Coccyx From IV. sacral nerve Coccypeus 



Dissection of female perineum, showing nerves; anal fascia in position on right side of body, removed on 

 left; Colics' fascia removed on right side, exposing superficial perineal interspace; superior layer of triangular 

 ligament, denuded of muscular tissue, seen on left side. 



nerve. Except in complete lc. ions of the spinal cord this nerve is rarely paralyzed 

 in all its branches. The paralysis may result from fractures of the lumbar vertebrae, 

 of the sacrum or of the innominate bone, frym pressure of tumors in the pelvis or of 

 the child's head in labor or from the use of forceps. It is the structure in greatest 

 'lander in dislocation of the hip, since the head of the femur in the most frequent 

 varieties sweeps backward against this nerve. In the reduction of these posterior 

 dislocations the nerve has been hooked up by the head and made to pass across the 

 front of the neck of the bone. From its close relation to the head and neck, it 

 may be injured in violent movements of the hip joint without dislocation. 



It passes out of the pelvis through the greater sacro-sciatic foramen, below the 

 pyrifonnis muscle, and after curving outward and downward under the gluteus maxi- 

 mus muscle it continues its course, approximately, in a line from a point midway 



