132 ANATOMY IN A NUTSHELL. 



THE FEMALE PELVIS DIFFERS FROM THE MALE PELVIS IN THE FOLLOWING 

 RESPE' I s: 



I | The bones are more slender. (2) ilia more vertical, (3) iliac fossa is 

 shallower, (4) false pelvis is relatively narrower, (5) the true pelvis is shallower, 

 also (6) true pelvis is wider, (7) inlet is more oval, (8) symphysis is shallower, 

 i'.ii tuberosities of ischia are everted. (10) pubic arch is wider and more round- 

 ed, ill) margins of ischio-pubic rami are less everted, (12) obturator foramen 

 is triangular, while in the male it is oval, (13) sacrum is wider and less curved, 

 and (14) the capacity of the true pelvis is greater. 



The Sacrum. 



The sacrum is formed by the coalescence of five segments. It forms the 

 upper and back part of the pelvis, being placed between the two innominate 

 bones. It is a wedge shaped bone with its apex below, and its anterior surface 

 wider than its posterior surface. 



The anterior border of the upper portion or base is called the promontory. 

 It has four surfaces, a base, an apex, and a central canal. 



The anterior surface has four ridges marking the junction of the five seg- 

 ments. This surface is concave, both vertically and transversely (less so.) 

 The five segments or vertebras decrease from above downward. At the ends of 

 the transverse ridges are foramina for the transmission of the sacral nerves. 

 These f< »ramina are directed forward and outward. At the sides of the foramina 

 are the lateral masses formed by the transverse processes of the vertebrae of 

 the sacrum. 



The posterior surface is not as wide as the anterior one and is convex. It 

 has rudimentary spinous processes in its median line. There are usually 

 three orfour of these, the fifth one being undeveloped. External to the processes 

 are the i.amive. the first three are well marked; the fourth is not well developed 

 and the fifth is rarely so. The fifth ones are prolonged downward forming the 

 sacral cornua. External to the laminae are the articular processes, the first 

 pair are Large, the second and third small, and fourth and fifth are most always 

 fused. Externa] to the articular processes are the foramina for the posterior 

 divisions of the sacral nerves. External to the foramina are the transverse 

 processes. 



The sacral groove is wide and shallow lodging the Erector spinas. It lies 

 between the spinous and transverse processes. 



The lateral surface is narrow behind but broad above. The upper half of 

 this surface is called the auricular surface. It articulates with the ilium and is 

 covered with fibro-cartilage in the recent state. Behind this articular surface 

 are deep impressions for the attachment of the posterior sacro-iliac ligaments. 

 The lower half of this surface is called the tuberosity, and the borders of this 

 half of the surface give attachment to the sacro-sciatic ligaments and part of 

 the ( rluteus maxiinus. 



The base is the pari which articulates with the last lumbar vertebra. It is 

 broad and look- upward and forward. Its anterior part is for the interarticular 

 fibro-cartilage and is oval. Its posterior part has the sacral canal which is 



