110 OUTLINES OF EQUINE ANATOMY. 



process about three inches downwards, is the inferior ilio- 

 sacral ligarnent, the fibres of which run obliquely down- 

 wards and backwards, to become attached inferiorly to the 

 transverse ridge of the sacrum, and to become continuous 

 onwards, blending with the substance of the sacrosciatic 

 ligament, after forming with that ligament below the trans- 

 verse ridge a canal extending from before, backwards, 

 through which an important branch of the gluteal artery, 

 with its accompanying vein and nerve, pass. The space on 

 the lateral part of the sacinim bounded outwardly by the 

 inferior ilio-sacral ligament and by the superior part of the 

 venter ilii is occupied by the posterior part of longissimus 

 dorsi, and when this is removed, a continuation of the 

 superior spinous ligament, under the form of a thick layer 

 of fibres running downwards and backwards over the lateral 

 surface of the sacral spines, is exposed. It is termed the 

 sacral ligament. 



The sacro-iliac ligament consists of a number of stout 

 ligamentous fibres, diverging in all directions from the 

 roughened surface around the auricular facet of the first 

 sacral transverse process. They run to the roughened 

 surface of venter ilii, and externally blend with the inferior 

 ilio-sacral ligament, internally being continuous with a stout 

 ligamentous band running towards the articulatory margin 

 on the anterior part of the last lumbar transverse process, 

 to the summit of which also a few scattered fibres run. 



The sacro-sciatic ligament forms the postero -lateral 

 boundary of the pelvis. Superiorly it is attached firmly 

 along the whole length of the transverse ridge of the 

 sacrum, inferiorly it becomes attached to the ischiatic spine, 

 and to the tuberosity of the ischium, from the line between 

 these two prominences becoming reflected inwards as a 

 fibrous layer between the jpelvic viscera, and the internal ohtu- 

 rator and pyriformis muscles becoming attached to the 

 superior edge of the posterior margin of the ischium and 

 along the upper part of the inner edge of the os innomi- 

 natum. Thus between the ligament and the bone are two 

 spaces ; the superior-ischiatic notch is between the anterior 

 margin of the ligament and the posterior margin of the 

 ilium, and gives passage to the gluteal vessels and nerve 

 and the sciatic nerve. The inferior-ischiatic notch between 

 the neck of the ischium and this ligament, where it is 

 reflected inwards, gives passage to the obturator internus 



