12 OBSTETRICAL ANATOMY. 



SECTION II. — ARTICULATIONS OF THE PELVIS. 



The bones of the pelvis are united by articulations and ligaments, as 

 well 48 fibrous bands, which are complementary, A knowledge of these 

 is of some importance to the obstetrist. The articulations are five in 

 number: (i) the sacro-lumbar, (2,3) the two sacro-iliac, (4) the ischio- 

 pubic symphysis, and (5) the sacro-coccygeal articulations. The ilio-sacral 

 and sacro-sciatic ligaments complete the subject of this section. 



I . Sacro-lumbar Articulation. 



The sacro-lumbar articulation is formed between the anterior face or 

 base of the sacrum, and the last lumbar vertebra j the union takes place 

 by five articular surfaces and thick fibro-cartilages, and numerous strong 

 ligaments bind the two bones closely and very firmly together, so as to 

 allow only a minimum amount of movement between them. It would 

 appear that these bones, though so limited in their movements on each, 

 yet are never anchylosed through old age, nor yet by accident, even if all 

 the other vertebrae in this region should happen to be consolidated. 



This arrangement is particularly remarkable in the Mare, on which it 

 confers great strength and solidity. It is not present in the Cow ; con- 

 sequently that animal is liable to a kind of incomplete luxation, which 

 may at times become an obstacle in parturition. 



We have already alluded to the salient angle formed by the union of 

 the last lumbar vertebra with the sacrum {sacra-vertebral angle), and 

 which looks downward into the abdominal cavity.* 



2, 3. Sacro-iliaC Articulations . 



The sacro-iliac articulation of each side establishes the union of the pos- 

 terior limbs with the spine, and is formed by the sacrum and ossa ilii ; it 



Fig. 4- 



Lateral Ligaments of the Sacrum and Pelvis. 



A, Superior Sacro-iliac Ligament ; B, Sacral Ligament ; C, Lateral Sacro-iliac Ligament ; 

 D, Sacro-sciatic Ligament ; E, Small Ischiatic Notch ; F, Great Ischiatic Notch. 



belongs to the arthrodial class of joints. The two surfaces which come into 

 opposition have been already described, and it only now remains to point 

 out that the sacrum is fixed between the antero-superior extremities of the 



* This angle is much more marked in woman, and is immediately at the entrance to the pelvis ; for 

 these reasons it is frequently a cause of difficult parturition in her, while, from its less development and 

 distance from the pelvis, it offers no obstacle in animals. 



