SACRO-VERTEBRAL AND SACRO-ILIAC ARTICULATIONS. 14? 



phalangeal articulations there is allowed, in addition, a movement of abduction and 

 adduction, but that chiefly in the extended position. In the articulation of the meta- 

 carpal bone of the thumb with the trapezium every movement is allowed except 

 rotation, which is prevented by the shape of the articular surfaces. 



ARTICULATIONS OF THE PELVIS. 



ARTICULATION OF THE PELVIS WITH THE LAST LUMBAR VERTEBRA. The 

 fifth lumbar is united to the first sacral vertebra by anterior and posterior 

 ligaments of the body, ligamenta subflava of the arch and interspinous 

 ligaments, and by an inter vertebral plate, all of which are similar to those 

 between the vertebrae above. It is also attached to the pelvis by two other 

 ligaments, as follows. 



The sacro-vertebral ligament extends obliquely from the tip of the trans- 

 verse process of the last lumbar vertebra downwards to the depressed lateral 

 part of the base of the sacrum ; its form is triangular, and its fibres diverge 

 as they descend, some of them joining the anterior sacro-iliac ligament. 



The ilio-lumbar ligament is extended horizontally between the summit of 

 the transverse process of the last lumbar vertebra and the iliac crest of the 

 innominate bone ; it is inserted into the latter at the back part of the iliac 

 fossa, where its fibres expand somewhat, so as to give it a triangular form. 



ARTICULATION OF THE SACRUM AND COCCYX, AND OP THE PIECES OF THE 

 COCCYX. These articulations are effected by an anterior ligament, consisting 

 of irregular fibres placed in front of the bones, a prolongation of the 

 anterior common ligament of the vertebrae ; by a posterior ligament more 

 strongly marked, composed of fibres which descend upon the bones of the 

 c >ccyx from the margin of the inferior orifice of the sacral canal ; and by 

 inter vertebral discs between the contiguous surfaces of the bones. 



A synovial membrane has been stated by Cruveilhier (" Anatomic descriptive," 

 torn. i. p. 356. Paris, 1834), to be present in those cases in which the coccyx is freely 

 moveable. This is in conformity with the more recent observations of Luschka on 

 the other intervertebral discs. In the male, after middle life, the union between the 

 sacrum and coccyx, and between the pieces of the latter, is usually ossific. In 

 the female this change does not generally occur till a more advanced age; the 

 pieces of the coccyx uniting one to another in the first place, and the joint between 

 the sacrum and coccyx not ossifying till old age. The mobility seems to increase 

 during pregnancy. 



THE SACRO-ILIAC ARTICULATION, often named the sacro-iliac synchondrosis, 

 is formed between the adjacent portions of the sacrum and ilium, the auri- 

 cular surfaces of which are coated with cartilage, and the remaining parts 

 are united by strong ligaments (see fig. 139). 



The auricular cartilaginous plate unites the bones with great firmness. 

 When the ilium and sacrum are forcibly torn asunder, this plate usually 

 separates into two layers, one of which adheres to the surface of each bone. 

 In some instances a small cavity naturally exists between these two plates 

 of cartilage. Even when separated in part, however, these plates are very 

 closely applied, and admit only a limited amount of movement. They are 

 then sometimes slightly united by delicate tissue, and in advanced life, small 

 spaces containing glairy fluid are liable to be formed between them. The 

 cavity of this articulation becomes more apparent, and the ligaments some- 

 what looser before parturition. 



The posterior sacro-iliac ligament, much the thicker, consists of a large 

 number of strong irregular fibres extending across the interval between the 

 posterior rough portion of the lateral surface of tho sacrum and that part of 



L 2 



