194 Joints of the Lower Extremity. 



Articulatio sacroiliaca (continued). It is strengthened on the posterior 

 surface by the ligamenta sacroiliaca interossea (see also Fig 1 . 245) and the ligamenta 

 sacroiliaca posteriora breve et longum. The latter form the broad mass of fibre 

 bands, only indistinctly separated from one another, which ascend obliquely from the 

 region of the crista sacralis lateralis of the sacrum toward the ala ossis ilium where 

 they are attached to the spinae iliacae posteriores and between them, the main mass 

 of them, especially the superficial bands, passing to the spina iliaca posterior superior; 

 of these the fibrous bands which come from the region of the second and third sacral 

 vertebra are called the ligamentum sacroiliacum postering breve, those from the region 

 of the fourth sacral vertebra, the ligamentum sacroiliacum posterius longum. These 

 ligaments cover over the ligamenta sacroiliaca interossea completely from behind and lie 

 close upon them. 



Of great importance for the form and firmness of the pelvis are also the liga- 

 mentum sacrotuberosum and the ligamentum sacrospinosum (see also 

 Fig. 243). 



The ligamentum sacrotuberosum (0. T. posterior or great sacrosciatic ligament) 

 arises broad and thin from the spinae iliacae posteriores superior et inferior as well as 

 from the lateral margin of the sacrum and of the two upper coccygeal vertebrae; it is 

 accordingly intimately connected in its upper part with the ligamenta sacroiliaca posteriora. 

 The fibres converge to form a strong flat ligament which extends obliquely forward, 

 downward and lateralward and becomes attached to the medial edge of the tuber 

 ischiadicum where it again broadens out; a narrow band which extends as a continuation 

 of some fibre bundles from this point along the medial margin of the ramus inferior 

 ossis ischii, is called the processus falciformis (0. T. falciform ligament). 



The ligamentum sacrospinosum (0. T. anterior or lesser sacrosciatic ligament) 

 is essentially thinner than the preceeding: it arises on the lateral margin of the lower 

 portion of the sacrum and of the upper coccygeal vertebrae, extends past the anterior 

 surface of the ligamentum sacrotuberosum forward and lateralward, narrowing as it goes, 

 and is attached to the spina ischiadica; at the point where it crosses the ligamentum 

 sacrotuberosum, it fuses with it. The ligamentum sacrospinosum forms, with the 

 m. coccygeus (see p. 328), a common mass of variable composition; sometimes the 

 connective tissue structures predominate, sometimes the muscle bundles. 



The ligamentum sacrotuberosum. as well as the ligamentum sacrospinosum, stretches 

 out median ward from the two incisurae ischiadicae (or between them) so that these 

 notches are transformed into foramina which are surrounded partly by bone, partly by 

 ligaments; the incisura ischiadica major becomes the rounded quadrangular foramen 

 ischiadicum majus (0. T. great sacrosciatic foramen), the incisura ischiadica minor 

 the triangular foramen ischiadicum minus (0. T. lesser sacrosciatic foramen) (see 

 also Fig. 243). 



