PELVIS. 



123 



from those in the pubic symphysis in being al- 

 most totally wanting in the fibrous elements 

 which are in the latter joint intermingled with 

 them. Under the microscope a section of the 

 sacro-iliac cartilages presents the ordinary ap- 

 pearance of cartifage incrusting the surfaces 

 of arthrodial joints. They have been said by 

 many writers to be completely incorporated 

 together so as to form but one mass; but such 

 is not the conclusion I have come to, except 

 in a few cases, after many examinations care- 

 fully made in subjects recently deceased. 

 The cartilages are very strongly adherent 

 to, and follow exactly the shape of, the auri- 

 cular articulating surfaces of the sacrum and 

 ilium before described, their rounded pro- 

 jecting angles being the most depending part 

 of the articulation. That on the sacrum is 

 almost double the thickness of the iliac 

 cartilage, which is somewhat less than one 

 eighth of an inch thick. In the male, in a few 

 instances, the two geem to project into each 

 other by irregular prominences, and to be con- 

 nected without the intervention of a regular 

 synovial membrane. In these cases it has been 

 remarked, that on the application of force, 

 the cartilage separates from the ilium, leaving 

 its auricular surface denuded. Much more 

 frequently in the male, however, and always 

 in the female and child, I have found, extend- 

 ing between them throughout, a completely 

 smooth surface, apparently lined by a delicate 

 membrane, and containing much thick synovia. 

 The opposing cartilaginous surfaces are, in 

 these cases, wavy or /-shaped, when seen in 

 a cross section, the sacral part being convex, 

 and the iliac part concave in front, the re- 

 verse arrangement having place behind, the 

 greatest depression being in the iliac surface, 

 exactly at the angular junction of the two 

 limbs of the auricular surfaces, at the most de- 

 pending point of the articulation, and through 

 which passes directly the line of pressure here- 

 after to be noticed (see fig. 89. page 144. 

 c,f). At this point also, the breadth of the 

 cartilaginous surface is the greatest, being 

 generally about an inch. Towards the extre- 

 mity of each limb the width gradually becomes 

 less. The inferior or horizontal portion is 

 longer than the other, generally being about 

 two inches long, the superior or vertical por- 

 tion being an inch and a half long. 



Immediately posterior to, or rather above, 

 this cartilage- covered surface, and filling up the 

 digital depressions found there on each bone, 

 are firmly implanted the inter-osseous ligaments, 

 composing the remainder of the articulation. 

 These consist of very strong and coarsely 

 interlacing fibres passing almost directly from 

 bone to bone, inclosing large meshes which 

 are filled with a soft loose synovial looking 

 fat, and containing many veins. Behind, 

 these are continued into the deep posterior 

 sacro-sciatic ligaments. 



The superior sacro-iliac ligament (fig. 80. a) 

 is a strong layer of fibres passing from the 

 lateral masses of the sacral base to the pos- 

 terior edge of the internal iliac fossa. It is 

 continued in front to the anterior sacro-iliac 



ligament (>), similar in character to the 

 last, but thinner and more feeble, passing 

 from the first three bones of the sacrum to 

 the superior border of the iliac notch. The 

 former of these assist to prevent downward 

 and backward displacement, and the latter 

 upward and backward displacement ; the 

 position of the former being more anterior 

 than superior, and the position of the latter 

 more inferior than anterior in the proper 

 position of the pelvis. 



By far the most powerful of the ligaments of 

 this articulation, and that which must be con- 

 sidered as the chief means of supporting the 

 great downward pressure at this joint, are the 

 posterior sacro -iliac ligaments. These are di- 

 vided into deep and superficial layers of fibres. 



The deep layer (fig. 89. page 144. e) passes 

 from a well-marked prominence on the anterior 

 surface of the iliac tuberosity, downwards and 

 inwards, to the superior lateral part of the pos- 

 terior surface of the sacrum, principally to the 

 two upper pieces, external to the foramina ; the 

 fibres spreading out in interlacing bundles to- 

 wards the broader surface of implantation on 

 the sacrum, becoming longer as they become 

 more superficial, and leaving meshes for the 

 interposition of masses of loose fat, and the 

 passage of numerous small veins. The erector 

 spinae muscles arise from the surface of this 

 ligament, and cover it. To obtain a good 

 view of these fibres, a transverse section along 

 the brim of the true pelvis should be carried 

 backward through the sacrum, as shown in 

 the figures. This will show the manner in 

 which the tuberosities of the ilium hang over 

 the sacrum, suspended, as it were, between 

 them by these ligaments. It will be more par- 

 ticularly explained when treating on the me- 

 chanics of the pelvis. The superficial posterior 

 sacro'iliac ligament (Jig. 8 1 ., next page, a) has 

 been termed oblique, from the direction of its 

 fibres ; or long, from the extent of them. It is 

 attached above to the posterior superior spine 

 of the ilium, and passes downwards and ob- 

 liquely a little inwards to be implanted jnto the 

 fourth transverse tubercle of the sacrum ex- 

 ternal to the hole. To the sides of this liga- 

 ment, which is almost subcutaneous, are at- 

 tached the fascia lumborum and great gluteus 

 muscle. This ligament is described by Cru- 

 veilhier to be attached to the third sacral 

 vertebra. In all the cases I have seen, it is 

 attached to the fourth transverse tubercle, 

 which is the most prominent tubercular pro- 

 jection in the dried bone. Bichat erroneously 

 calls it " sacro-spinous." 



Attached to the same sacral tubercle, and 

 passing horizontally outwards to be im- 

 planted into the posterior surface of the in- 

 ferior posterior spine of the ilium, a point 

 exactly corresponding to the termination of 

 the horizontal limb of the sacro-iliac articular 

 surface, is another well-marked ligament 

 (fig. 81. b), which, being separated by a dis- 

 tinct cellular interval from the deep ligaments 

 and distinguished by the more deeply seated 

 position and horizontal direction of its fibres 

 from the oblique ligament (a), and from the 



