82 OUTLINES OF EQUINE ANATOMY. 



BONES OF THE HIND LIMB. 



The posterior cavity of tlie "body is termed ttie pelvis. It 

 is most marked in tlie skeleton for in tlie fresli subject it is 

 anteriorly confounded witli the posterior part of the abdo- 

 men. Its basement structure consists of two bones (each 

 composed of smaller portions connected together by liga- 

 ments), superiorly is the sacrum which has been described as 

 part of the spinal column. Inferiorly and lateral^ are the 

 ossa innominata. 



OSSA INNOMINATA are two in number, one on each 

 side, and these are united at the inferior part centrally 

 forming the symjohysis. These bones originally consist 

 each of three parts, but in the adult these parts are firmly 

 united to form one bone. Supero-anteriorly is the ilium 

 forming the lateral boundary of the pelvis at the ante- 

 rior part; antero-inferiorly is os pubis; postero -inferiorly 

 OS ischium. The three unite in forming a cotyloid cavity 

 termed the acetabulum, coated with articular cartilage 

 with a gap extending from its inner and anterior part 

 towards the centre, where ligamentum teres which serves 

 to maintain the cavity in contact with the head of the 

 femur, is attached. It is deep in all parts and is rendered 

 more so by a band of fibro-cartilage (circumferential or 

 cotyloid) which is attached around its margin, and is con- 

 tinued across the gap forming the transverse ligament, 

 and binding down the pubio-femoral ligament in its 

 passage to the head of the femur. The ischium forms 

 the major portion of this cavity (about three-fifths), while 

 the pubis forms the least, a little less than one-fifth, os 

 ilium forming a little more than one-fifth ; but a consider- 

 able j)art of the pubis is occupied by the roughened 

 groove extending inwards. The acetabulum looks outwards 

 and slightly downwards and backwards. 



OS ILIUM is a flat bone, triangular in shape, placed 

 obliquely from above downwards and outwards. It is tri- 

 angular, and presents two surfaces, three margins, and three 

 angles. The antero -inferior angle is termed the antero- 

 inferior spinous process, it is rough and tuberous, elongated 

 from above downwards presenting four prominences, two 

 superiorly, two inferiorly. It affords attachment internally 

 to iliacus, longissimus dorsi, obliquus abdominis externus, 

 obliquus abdominis internus, transversalis abdominis, and 



