ARTICULATIONS OF TEE POSTERIOR LIMBS. 



213 



lateral, and permits its circumference to be divided into four borders : a suj^erior, 

 attached to the rugged lateral ridge of the sacrum ; an inferior, fixed to the supra- 

 cotyloid ridge, as well as the ischial tuberosity, and forming by the portion 

 comprised between these two insertions, with the small ischiatic notch, the opening 

 by which the internal obturator and pyramidalis muscles leave the pelvis ; an 

 anterior, imperfectly limited, along with the great sciatic notch, circumscribes 

 the opening through which the ghiteal vessels and nerves, and the sciatic nerves 

 pass ; a posterior, doubled in the form of two layers which embrace the semi- 

 membranosus muscle, and is confounded superiorly with the aponeurosis envelop- 

 ing the coccygeal muscles. The external face of this ligament is traversed by the 

 sciatic nerves, and is covered by the long vastus and the semitendinosus muscles, 

 which derive numerous insertions from it. Its internal face is covered, in front, 



SACRO-ILIAC AND COXO-FEMORAL ARTICULATIONS, WITH THEIR SURROUNDIHG MUSCLES. 



11, Sacro-sciatic ligament; 12, great sciatic notch; 13, superior ilio-sacral ligament; 14, inferior 

 ilio-sacral ligament. 



by the peritoneum, and, posteriorly, is in contact with the ischio-coccygeal and 

 ischio-anal muscles, to which it gives attachment. 



Si/novial memhrane. — This lines the sacro-iliac ligament, but only furnishes a 

 small quantity of synovia. 



MovemenU. — The two sacro-iliac articulations, being the centres towards which 

 all the propulsive efforts communicated to the trunk by the posterior limbs con- 

 verge, do not offer much mobility, as that would oppose the integral trans- 

 mission of the propulsion. So that they permit only a very restricted gliding of 

 the articular surfaces ; while the union of the sacrum and coxa by diarthrosis, 

 appears to be exclusively designed to prevent the fractures to which these bones 

 would be incessantly exposed, if they were fixed together in a more intimate 

 manner. 



B. Articulation of the two Cox^, or Ischio-pubic Symphysis. — The 

 two coxffi are united to each other throughout the whole extent of the inner border 

 of the pubis and the ischial bones. In youth, this is a veritable amphiarthrosis, 

 fixed by an interosseous cartilage and bundles of peripheral fibres. 



The cartilage is solidly fixed to the small rugged eminences which cover the 

 adjacent articular surfaces, and becomes ossified, like the sutural cartilages, as 



