350 HUMAN ANATOMY. 



internal to the external abdominal ring, and is on the outer side of an inguinal 

 hernia and on the inner side of a femoral hernia. 



With the finger in the rectum, the tip of the coccyx and a little of the anterior 

 curve can be felt, as well as the small sacro-sciatic ligaments leading to the ischial 

 spines. Laterally, the tuberosities of the ischium, the smooth bone forming the 

 wall of the pelvis, and the structures back of the acetabulum (page 1693) can be 

 palpated. 



Through the vagina the configuration of the subpubic arch can be felt, also 

 the pelvic wall to either side. If the promontory of the sacrum can be touched, 

 it indicates deformity accompanied by diminution of the antero-posterior pelvic 

 diameter. 



With the hand in the rectum, the brim of the pelvis, the arch of the pubes, the 

 sacral promontory, the curve of the sacrum and coccyx, the spines of the ischium, 

 and the margins of the sacro-ischiatic foramina can be palpated. 



The Joints of the Pelvis. — The sacro-hunbar joint has a wider range of 

 movement than any of the joints between the contiguous dorsal or lumbar verte- 

 brae. This is due to the greater thickness of the intervertebral substance, permit- 

 ting flexion and extension, and to the fact that the inferior articulating processes 

 point more antero-posteriorly than those of the other lumbar vertebrae, thus admit- 

 ting of more rotation on a vertical axis. 



In spite of this, on account of the strength of the ligaments of the joint, and 

 more particularly for the reasons that tend to localize the effect of traumatism some- 

 what higher in the spine (page 145), sprain and disease of the sacro-lumbar articu- 

 lation are both uncommon. 



Overextension of the joint is brought about if with the body prone the shoul- 

 ders are raised while the hips are fixed. Pain thus produced suggests lumbar or 

 sacro-lumbar disease, as in sacro-iliac disease this movement is often painless. 



The sacro-coccygeal joint is not infrequently strained by falls upon the buttocks, 

 and occasionally the coccyx is displaced forward. The joint is sometimes the subject 

 of disease. The symptoms are very similar in all these conditions. The attachment 

 of the gluteus maximum makes a change from a sitting to a standing posture or the 

 reverse movement painful ; it also causes pain if long steps are taken or if running 

 is attempted, and this is aggravated by the action of the hamstring muscles through 

 the medium of the great sacro-sciatic ligament. As the fixed point of the external 

 sphincter is at the tip of the coccyx, and as the levator ani is inserted into the sides 

 of the tip, defecation is associated with movement in this joint, and therefore with 

 pain. The latter is often disproportionate to the apparent severity of the injury or 

 disease, and there may be also great tenderness to the touch posteriorly, with no swell- 

 ing or local heat. As these cases chiefly occur in women, Hilton thinks that they 

 are truly "hysterical," and calls attention to the intimate structural communication 

 between the many sacral nerves spread over the posterior surface of the sacrum and 

 coccyx and the anterior sacral nerves, which join with the hypogastric plexus of the 

 sympathetic within the pelvis and thence proceed to the uterus and ovaries. 



The motion of the sacro-coccygeal joint is of great importance in its relation 

 to obstetrics. Ankylosis occurs, as a rule, between the thirtieth and fortieth years, 

 but the joint between the first and second sacral vertebrae usually remains unaffected, 

 and leaves the capacity for antero-posterior expansion during labor practically un- 

 impaired. 



The Sacro- Iliac Joint. — Injury to and disjunction of this joint have been suffi- 

 ciently described under Fractures of the Pelvis (page 347). 



Disease of the joint, on account of its strength and immobility, is rare. It is 

 usually tuberculous in character, and is often secondary to suppuration beneath the 

 ilio-psoas from disease of the spine, ilium, or hip. Pain is felt on standing, walking, 

 or sitting, as the sacrum in all these positions bears the weight of all the super- 

 incumbent structures, and on account of its shape (page 346) transmits it to the 

 sacro-iliac synchondrosis. The pain is increased by coughing, straining, or twisting 

 the loins, — i.e., by whatever calls into action the muscles attached to the ilium. 

 Through the relation of the superior gluteal nerve to the front of this joint, pain is 

 often felt in the buttock, and there is wasting of the deep gluteal muscles. The 



