LIGAMENTS OF THE PELVIS. 117 



which completes the lower part of the sacral canal, and connects 

 the sacrum with the coccyx posteriorly, extending as far as the apex 

 of the latter bone. 



Between the two bones is a thin disc of a soft intervertebral sub- 

 stance. In females there is frequently a small synovial membrane. 

 This articulation admits of a certain degree of movement backwards 

 during parturition. 



The ligaments connecting the different pieces of the coccyx con- 

 sist of a few scattered anterior and posterior fibres, and a thin disc 

 of intervertebral substance ; they exist only in the young subject, in 

 the adult the pieces become ossified. 



4. Between the Ossa Pubis. The anterior pubic ligament is com- 

 posed of ligamentous fibres, which pass obliquely across the union of 

 the two bones from side to side, and form an interlacement in front of 

 the symphysis. 



The posterior pubic ligament consists of a few irregular fibres 

 uniting the pubic bones posteriorly. 



The superior pubic ligament is a thick band of fibres connecting 

 the angles of the pubic bones superiorly, and filling the inequalities 

 upon the surface of the bones. 



The sub-pubic ligament is a thick arch of fibres connecting the 

 two bones inferiorly, and forming the upper boundary of the pubic 

 arch. 



The interosseous jibro-cartilage unites the two surfaces of the pubic 

 bones, in the same manner that the intervertebral substance con- 

 nects the bodies of the vertebrae. It resembles the intervertebral 

 substance also in being composed of oblique fibres disposed in con- 

 centric layers, which are more dense towards the surface than near 

 the centre. It is broad in front, and narrow behind. A thin syno- 

 vial membrane is sometimes found in the posterior half of the articu- 

 lation. 



This articulation becomes movable towards the latter term of preg- 

 nancy, and admits of a slight degree of separation of its surfaces. 



The obturator ligament or membrane is not a ligament of articula- 

 tion, but simply a tendino-fibrous membrane stretched across the 

 obturator foramen. It gives attachment by its surfaces, to the two 

 obturator muscles ; and leaves a space in the upper part of the fora- 

 men, for the passage of the obturator vessels and nerve. 



The numerous vacuities in the walls of the pelvis, and their clo- 

 sure by ligamentous structures, as in the case of the sacro-ischiatic 

 fissures and obturator foramina, serve to diminish very materially 

 the pressure of the soft parts during the passage of the head of the 

 foetus through the pelvis in parturition. 



LIGAMENTS OF THE UPPER EXTREMITY. 



The Ligaments of the upper extremity may be arranged in the 

 order of the articulation between the different bones ; they are, the 



