THE HORSE. 
extremities to the impressions around the articular surfaces, situated 
so the sacrum and internal border of the ilium. The inferior half of 
this ligament is covered by the psoas muscles. Its posterior half, much 
stronger than the former, is hidden by the ilium. 
The superior alio-sacral ligament is a large, strong, short ligament, 
which, arising from the internal part of the ‘lium, i is carried backwards 
and fixes itself upon the sacral spines, where it mixes its fibres with the 
supra-spinous ligament of the Jumbar vertebre. 
The inferior tlio-sacral ligament is a triangular and very resisting mem- 
branous band, formed of parallel fibres running obliquely from above 
downwards, and from before backwards. It is attached by its antero- 
inferior edge to the superior half of the ischiatic border and the internal 
angle of the ilium, mixing itself with the preceding ligament ; its superior 
border inserts itself upon the roughened ridge which bounds the sacrum 
laterally ; its posterior border is united to the aponeuroses which cover 
the coccygeal muscles. 
The sacro-sciatic ligament is a vast membranous expansion, stretched 
upon the side of the pelvis, between the sacrum and the os innominatum ; 
it serves rather as an inclosure for the pelvic cavity than as a means of 
securing the firmness of the sacro-iliac articulation. Its form is irregu- 
larly quadrilateral, presenting four borders-—a superior, attached to the 
lateral roughened edge of the sacrum ; an inferior, inserted in the ridge 
below the. cotyloid “cavity ; 3 an anterior, unattached in a great part of 
its course, and serving as a protection to the large vessels and nerves 
which pass through the sciatic notch ; and lastly, a posterior margin, which 
splits into two lamine, between which the semi-membranous muscle takes 
its origin. 
A synovial membrane covers the sacro-iliac ligament, but furnishes a 
small quantity of synovia. 
Movements.—The two sacro-iliac articulations, through which all the 
efforts of impulsion are communicated to the trunk by the posterior 
members, without interfering with the transmission of locomotive force, 
permit but a slight gliding movement of their arthrodial surfaces. Indeed, 
this articulation seems exclusively designed to prevent the fractures to 
which these bones would be incessantly exposed, were they attached in 
a more intimate manner, as, for example, by bony union. 
ISCHIO-PUBIC SYMPHYSIS. 
THE TWO OSSA INNOMINATA are firmly united together in the median 
line below, by the corresponding edges of the ischium and pubes. In 
the foal this is a distinct joint, possessing an inter-articular cartilage, and 
some transverse ligamentous fibres above and below ; but in the adult horse 
the two bones are firmly united by ossification, and the ossa innominata 
together form a complete arch, without the slightest movement between 
them. 
THE SHOULDER JOINT. 
THE SCAPULO-HUMERAL ARTICULATION, commonly known as the shoulder 
joint, belongs to the division Diarthrosis ; subdivision, Enarthrosis. It 
is formed by the scapula uniting with the humerus, at an obtuse angle. 
THE ARTICULAR SURFACES which compose this joint are the head of the 
humerus, and the glenoid cavity of the scapula. On examining these 
bones, described and illustrated at page 336, it will be seen that the 
head of the humerus is semi-globular, while the cavity in the scapula is 
