PRACTICAL CONSIDERATIONS : THE PELVIS. 



349 



Fig. 368. 



sometimes resembles the tail of lower animals. They frequently arise from the an- 

 terior part of the coccyx behind the rectum, and contain muscular, bony, epithelial, 

 or cartilaginous elements in an imperfect and fragmentary condition. When a third 

 lower limb is found connected with this part of the pelvis, the condition is known as 

 ' ' tripodism. " 



In some of the reported cases of parasitic foetuses the point of junction has been 

 in this region. 



Sinuses over the sacrum and coccyx occasionally persist after abscesses following 

 blows or falls. If the pus has travelled in a lateral direction, the suppurating track 

 will be found to lead to the region of origin of the tendinous sacral apd coccygeal 

 fibres of the gluteus maximus. The probe may catch against these points and give 

 a kind of grating sound, like that due to bare or dead bone. The continuance of the 

 sinuses is not the result of necrosis, but is due to the unyielding character of the 

 tendinous structures. This prevents apposition and union of the sinus walls until 

 tension has been removed. 



Landmarks. — Anteriorly, the anterior superior spinous process of the ilium is 

 most easily recognized as a prominence at the outer end of the fold of the groin. 

 In very fat subjects its situation is indicated by an oblique, slightly elongated de- 

 pression. It is a little above the level of the promontory of the sacrum. Running 

 upward and outward and curving backward in an irregularly S-shaped line is the 

 iliac crest. In muscular subjects the fibres of the 

 external oblique overhang the crest, causing a crease 

 in the soft parts which lie between these fibres and 

 those of the gluteus medius a little below the level of 

 the crest ; it is known as the " iliac furrow." It is less 

 marked where the crest passes below the tendinous 

 portion of the erector spinae. 



The posterior superior spine is not so prominent 

 as the anterior, but may easily be found by following 

 the crest to its posterior termination. Its position is 

 indicated by a slight depression on the surface on a 

 level with the second sacral spine and behind the 

 middle of the sacro-iliac joint. The third sacral spine 

 lies just below in the mid-line, and indicates the level 

 to which the membranes of the cord enclose a distinct 

 space, and, therefore, the lowest point at which cerebro- 

 spinal fluid can be found. The curve of the sacrum 

 and coccyx may be traced to the tip of the latter. 



The ischial tuberosities are easily felt when the 

 hip is flexed and the fibres of the gluteus maximus are 

 thus withdrawn. A bursa is interposed between them 

 and the layer of subcutaneous fat which covers them. 

 They can be felt, but with more difficulty, through 

 the gluteus fibres when the hip is in extension. Five 

 centimetres (two inches) below the posterior superior 



spine, on a line drawn from it to the outer part of the tuberosity, lies the pos- 

 terior inferior spine, and five centimetres (two inches) lower still the spine of the 

 ischium. The sciatic and internal pubic arteries emerge at the junction of the 

 lower and middle thirds of this line. The pudic artery crosses the spine of the 

 ischium on its way between the great and small sacro-sciatic foramina. A line, 

 called Nelaton's, drawn from the anterior superior spine to the prominence of the 

 tuber touches the top of the greater trochanter and crosses the centre of the ace- 

 tabulum (Fig. 368). 



The pubic symphysis may be felt indistinctly and the horizontal rami more 

 easily. 



The pubic spine is readily felt in thin persons. In fat males it may be most 

 easily found by invaginating the scrotum. In either sex the tendon of the adductor 

 longus — made tense by abducting the thigh — is an unfailing guide to it. It lies on 

 the level of the upper edge of the greater trochanter. It is just below and a little 



Diagram showing Nelaton's line. 



