311 



The Interpubic Fibrocartilaginous Lamina (lamina fibrocartilaginea interpubica; 

 interpubic disk). The interpubic fibrocartilaginous lamina connects the opposed 

 surfaces of the pubic bones. Each of these surfaces is covered by a thin layer of 

 hyaline cartilage firmly joined to the bone by a series of nipple-like processes which 

 accurately fit into corresponding depressions on the osseous surfaces. These 

 opposed cartilaginous surfaces are connected together by an intermediate lamina 

 of fibrocartilage which varies in thickness in different subjects. It often contains 

 a cavity in its interior, probably formed by the softening and absorption of the 

 fibrocartilage, since it rarely appears before the tenth year of life and is not lined 

 by synovial membrane. This cavity is larger in the female than in the male, but 

 it is very doubtful whether it enlarges, as was formerly supposed, during pregnancy. 

 It is most frequently limited to the upper and back part of the joint; it occasion- 

 ally reaches to the front, and may extend the entire length of the cartilage. It may 

 be easily demonstrated when present by making a coronal section of the symphysis 

 pubis near its posterior surface (Fig. 321). 



Ant. sup. iliac 



Obturalor canal 

 Lacunar ligament 

 Pubic tubercle 



Jnierpubic 



fibro- 

 cartilaginous 

 lamina 



Transverse acetabular 

 ligament 



FIG. 321. Symphysis pubis exposed by a coronal section. 



Mechanism of the Pelvis. The pelvic girdle supports and protects the contained viscera and 

 affords surfaces for the attachments of the trunk and lower limb muscles. Its most important 

 mechanical function, however, is to transmit the weight of the trunk and upper limbs to the 

 lower extremities. 



It may be divided into two arches by a vertical plane passing through the acetabular cavities; 

 the posterior of these arches is the one chiefly concerned in the function of transmitting the 

 weight. Its essential parts are the upper three sacral vertebrae and two strong pillars of bone 

 running from the sacroiliac articulations to the acetabular cavities. For the reception and diffu- 

 sion of the weight each acetabular cavity is strengthened by two additional bars running toward 

 the pubis and ischium. In order to lessen concussion in rapid changes of distribution of the 

 weight, joints (sacroiliac articulations) are interposed between the sacrum and the iliac bones; 

 an accessory joint (pubic symphysis) exists in the middle of the anterior arch. The sacrum forms 

 the summit of the posterior arch; the weight transmitted falls on it at the lumbosacral articula- 

 tion and, theoretically, has a component in each of two directions. One component of the force 

 is expended in driving the sacrum downward and backward between the iliac bones, while the 

 other thrusts the upper end of the sacrum downward and forward toward the pelvic cavity. 



