160 / //A' ARTICULATIONS. 



tho ischiatic border and tho internal anglu uf tho ilium, in becoming 

 confounded with tho preceding ligament. Its inferior margin is inserted 

 into tho rugged lip which borders the sacrum laterally. Its posterior bonier 

 is united to the aponeurosis covering tho coccygcal muscles, and its external 

 face is in contact with the principal gluteal and tho long vastus muscles ; 

 while the internal corresponds to the lateral sacrc-coccygeal muscle. 



d. Sacro-sciatic or ischiatic llyament (Fig. 90, 2). This is a vast mem- 

 branous expansion situated on the side of tho pelvis, between the sacrum 

 and tho coxa, and serves more as a means for inclosing this portion of tho 

 pelvic cavity than to assure tho solidity of tho sacro-iliac articulation. Its 

 form is irregularly quadrilateral, and permits its circumference to be divided 

 into four borders : a superior, attached to the rugged lateral ridge of tho 

 sacrum ; an inferior, fixed to tho supercotyloid ridge, as well as the ischial 

 tuberosity, and forming by tho portion comprised between these two in- 

 sertions, with the small ischiatic notch, tho opening by which the internal 

 obturator and pyramidal muscles leave the pelvis ; an anterior, imperfectly 

 limited, along with the great ischiatic notch, circumscribes the opening 

 through which tho gluteal vessels and nerves, and the sciatic nerves pass ; a 

 posterior, doubled in the form of t\\o lamina* which embrace the semi- 

 membranosus muscle, and is confounded superiorly with the nponeurosis 

 enveloping the coccygoal muscles. Tho external face of this ligament is 

 traversed by the sciatic nerves, aud is covered by tho long vastus and the 

 semitendinosus muscles, which derive numerous insertions from it. Its 

 internal face is covered, in front, by tho peritoneum, and posteriorly is in 

 contact with the ischio-coccygeal and ischio-anal muscles, to which it gives 

 attachment. 



Synovial membrane. This lines tho sacro-iliac ligament, but only 

 furnishes a small quantity of synovia. 



Movements. The two sacro-iliac articulations being tho centres towards 

 which all the impulsive efforts communicated to the trunk by the posterior 

 limbs converge, they do not offer much mobility, as that would oppose 

 the integral transmission of the quantity of movement. So that they 

 permit only a very restricted gliding of the articular surfaces; and tho 

 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 COXJE, on ISCHIO-PUBIO SYMPHYSIS. The 

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

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

 amphiarthrosis, fixed by an iuterosscous oartilage 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 tho sutural 

 cartilages, as tho animal advances in ago. In adult Solipeds the coxtu are 

 always fused with each other. 



The peripheral fibrous fasciculi extend tranversely from one bone to 

 the other, above and below tho symphysis ; thoso on the inferior face are 

 incomparably stronger and more abundant than tho others. 



The movements of this articulation are most restricted, and depend 

 solely upon the elasticity of tho interosscous cartilage. They cease after its 

 ossification. 



The fusion of the two coxee proceeds very slowly in the/ema/ of the Cat, Dog, /'/./, 

 Ox, Sheep, and Goat species. 



