THE COXO-FEMORAL OR HIP JOINT 89 



and circumduction. The joint is formed by the reception of the 

 articular head of the femur into the cotyloid cavity of the innominate 

 bone. 



The cotyloid cavity is a depression with an almost circular boundary. 

 The cavity is placed in the position v\^here the ilium, ischium, and pubis 

 meet, and all these bones therefore enter into its formation, though in 

 varied proportion. The rim of the cavity is not complete, being inter- 

 rupted towards its inner side by a well-marked notch. The interior of 

 the cavity is entirely articular with the exception of a triangular area 

 which extends from the before-mentioned notch in the rim, towards the 

 centre of the cavity, the base of the triangle being directed towards 

 the notch, and the apex therefore inwardly. Apart from this 

 triangular roughened area, the cotyloid cavity is covered by articular 

 cartilage. 



The articular head of the femur is a smooth, hemispherical eminence, 

 which is placed towards the inner side of the bone. It is so moulded 

 as to be accommodated in the cotyloid cavity, and, like the latter, is 

 wholly articular with the exception of a triangular outcut placed towards 

 its inner side. 



The ligaments of the hip joint are as follows : 



(a) Pubio-Femo7'aL — This is a ligament which is peculiar to the 

 horse tribe. It is in the form of a flattened band which arises from the 

 prepubic tendon of the abdominal muscles of the opposite side of the 

 body. It runs first obliquely backwards and outwards, crossing its fellow 

 ligament on the median line. Its course is next directed transversely 

 outwards along the pubio-femoral groove on the inferior aspect of the 

 pubic bone. Passing through the notch in the rim of the acetabulum, 

 it runs to its insertion into the non-articular sulcus in the head of the 

 femur. To arrive at its insertion it has to pass therefore, as we shall 

 see later, over the transverse ligament. 



This ligament, owing to the manner of its disposition, materially 

 restricts the degree of abduction of the hip joint in the horse. It is 



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