OF THE PELVIS. 339 



posterior border of the os innominatum ; behind, by the great sacro-sciatic ligament ; 

 and below, by the lesser sacro-sciatic ligament. It is partially filled up, in the 

 recent state, by the Pyriformis muscle, which passes through it. Above this muscle 

 the gluteal vessels and superior gluteal nerve emerge from the pelvis, and, below 

 it. the sciatic vessels and nerves, the internal pudic vessels and nerve, and muscular 

 branches from the sacral plexus. The inferior or lesser sacro-sciatic foramen is 

 bounded, in front, by the tuber ischii ; above, by the spine and lesser sacro-sciatic 

 ligament ; behind, by the greater sacro-sciatic ligament. It transmits the tendon 

 of the Obturator internus muscle, its nerve, and the internal pudic vessels and 

 nerve. 



3. ARTICULATION OF THE SACRUM AND COCCYX. 



This articulation is an arthrodial joint, and is formed between the oval sur- 

 face at the apex of the sacrum and the base of the coccyx. It is connected by 

 the following ligaments : 



Interarticular. 



Anterior Sacro-coccygeal. Lateral Sacro-coccygeal. 



Posterior Sacro-coccygeal. Interposed Fibro-cartilage. 



The Interarticular Ligaments connect the cornua of the two bones. 



The Anterior Sacro-coccygeal Ligament consists of a few irregular fibres which 

 descend from the anterior surface of the sacrum to the front of the coccyx, becom- 

 ing blended with the periosteum. 



The Posterior Sacro-coccygeal Ligaments are the superficial and the deep. The 

 superficial is a flat band of ligamentous fibres, of a pearly tint, which arises from 

 the margin of the lower orifice of the sacral canal and descends to be inserted 

 into the posterior surface of the coccyx. This ligament completes the lower and 

 back part of the sacral canal. The deep consists of a few fibres, which descend 

 to the coccyx from that part of the sacrum which forms the anterior wall of the 

 lower part of the sacral canal. Its lower end blends with the preceding. 



The Lateral Sacro-coccygeal Ligaments are ligamentous bands, each of which 

 passes from the inferior lateral angle of the sacrum to the transverse process of 

 the first piece of the coccyx. 



A Fibro-cartilage is interposed between the contiguous surfaces of the sacrum 

 and coccyx. It is somewhat thicker in front and behind than at the sides. Occa- 

 sionally, a synovial membrane is found when the coccyx is freely movable, which 

 is more especially the case during pregnancy. 



The different segments of the coccyx are connected together by an extension 

 downward of the anterior and posterior sacro-coccygeal ligaments, a thin annular 

 disk of fibro-cartilage being interposed between each of the bones. In the adult 

 male all the pieces become ossified, but in the female this does not commonly 

 occur until a later period of life. The separate segments of the coccyx are first 

 united, and at a more advanced age the joint between the sacrum and coccyx is 

 obliterated. 



Actions. The movements Avhich take place between the sacrum and coccyx, 

 and between the different pieces of the latter bone, are slightly forward and 

 backward ; they are very limited. Their extent increases during pregnancy. 



4. ARTICULATION OF THE OSSA PUBIS (Fig. 241). 



The articulation between the pubic bones is an amphiarthrodial joint, formed 

 by the junction of the two oval articular surfaces of the ossa pubis. The articular 

 surface has been described on a former page under the name of symphysis, and the 

 same name is given to the joint. The ligaments of this articulation are the 



Anterior Pubic. Posterior Pubic. 



Superior Pubic. Subpubic. 



Interpubic disk. 



