282 THE ARTICULATIONS OR JOINTS. 
last lumbar vertebra, downwards and slightly outwards, to the front of the lateral 
aspect of the ala of the sacrum, close to the sacro-iliac joint. Further, a variable 
membranous band extends between the lateral aspect of the lower part of the body 
of the last lumbar vertebra and the front of the ala of the sacrum. This band lies 
in front of the anterior primary division of the fifth lumbar nerve. 
SACRO-ILIAC JOINT. 
Each innominate bone articulates with the sacral section of the spimal column 
on each side through the intervention of a diarthrosis, termed the sacro-iliae joint 
(articulatio sacroiliaca). 
This joint is formed between the contiguous auricular surfaces of the sacrum 
and ilium. Each of these surfaces is more or less completely clothed by hyaline 
articular cartilage. The joint-cavity, which is little more than a capillary interval, 
may be crossed by fibrous bands. 
The joint-cavity is surrounded by ligaments of varying thickness and strength, 
which constitute its capsule. Thus the anterior part of the investing capsule is 
thin, and con- 
sists of short 
Anterior common ligament aa 9 / Inferior ilio-lumbar ligament but strong 
oe Lumbo saeral fibres which 
pe lenment pass between 
adjoining sur- 
faces on the ala 
Anterior 
sacro. Of the sacrum@ 
ligement 200 the iliae 
fossa of the 
innominate 
Nlio-luinbar ligaments 
Great sacro- 
sciatic ligament 
Small sacro- 
sciatic ligament Tlio- bone; the Vi 
/trochanteric 4 d 
Cotyloid “ ligament form the 
ligament 
anterior sacro- 
,__Tlio- iliac ligament 
«femoral 3 ve 
ligament (lig. sacro-ilia- 
cum anterius, 
Fig. 219). On 
Capsule 
= Transverse 2 Anterior 5 2 ReH the posterior 
=8 acetabular 32 pubic Ys eo 
Be ligament &s liga- ES ES aspect there 
= & " Ya fay) . 
= Steg ics wee are two liga- 
ee = Sele is : 
= = 5 ments. Dhe 
i short posterior 
Fig. 219.—PrEtvic JOINTS AS SEEN FROM THE FRONT. sacro-iliac liga- 
mi ment (lig. 
sacro-iliacum posterius breve, Fig. 220) consists of numerous strong fasciculi, 
which pass from the rough area on the inner aspect of the ilium, above and behind 
its auricular surface, downwards and inwards to the transverse tubercles and the 
depressions behind the first and second segments of the sacrum. ‘This ligament 
is of great strength, and with its fellow it is responsible for suspending the 
sacrum and the weight of the superimposed trunk from the innominate bones. 
The long or oblique posterior sacro-iliac ligament (lig. sacro-iliacum posterius 
longum, Fig. 220) is a superficial thickened portion of the preceding ligament. 
It consists of a definite band of fibres passing from the postero-superior iliac spine 
to the transverse tubercles of the third and fourth segments of the sacrum. 
The synovial cavity of this joint is very imperfect and rudimentary. 
Several accessory ligaments are associated with the articulation of the in- 
nominate bone to the sacral section of the spinal column. 
The ilio-lumbar ligament (lig. ilio-lumbale, Fig. 219), which is merely the 
thickened anterior lamina of the fascia lumborum, extends from the tip of the 
transverse process of the last lumbar vertebra, almost horizontally outwards, to the 
inner lip of the iliac crest at a point a short distance behind its highest level. 
