176 THE SKELETON. 



the Semimembranosus ; from the lower and inner, the Biceps and Semiten- 

 dinosus. 



The ramus is the thin, flattened part of the ischium Avhich ascends from the 

 tuberosity upward and inward, and joins the descending ramus of the os pubis, 

 their point of junction being indicated in the adult by a rough line. The outer 

 surface of the ramus is rough, for the attachment of the Obturator externus 

 muscle, and also some fibres of the Adductor magnus ; its inner surface forms 

 part of the anterior wall of the pelvis. Its inner border is thick, rough, slightly 

 everted, forms part of the outlet of the pelvis, and presents two ridges and an 

 intervening space. The ridges are continuous with similar ones on the descend- 

 ing ramus of the os pubis : to the outer one is attached the deep layer of the 

 superficial perinea! fascia, and to the inner, the superficial layer of the triangular 

 ligament of the urethra. If these two ridges are traced downward, they will be 

 found to join with each other just behind the point of origin of the Transversus 

 perinaei muscle; here the two layers of fascia are continuous behind the posterior 

 border of the muscle. To the intervening space, just in front of the point of 

 junction of the ridges, is attached the Transversus perinrei muscle, and in front 

 of this a portion of the crus penis vel clitoridis and the Erector penis vel 

 clitoridis muscle. Its outer border is thin and sharp, and forms part of the inner 

 margin of the obturator foramen. 



The Os Pubis forms the anterior part of the os innominatum, and, with the bone 

 of the opposite side, forms the front boundary of the true pelvic cavity. It is 

 divisible into a body, an ascending and a descending ramus. 



The body is somewhat quadrilateral in shape, and presents for examination 

 two surfaces and three borders. The anterior surface is rough, directed down- 

 ward and outward, and serves for the attachment of various muscles. To the 

 upper and inner angle, immediately below the crest, is attached the Adductor 

 longus ; lower down, from without inward, are attached the Obturator externus, 

 the Adductor brevis, and the upper part of the Gracilis. The posterior surface, 

 convex from above downward, concave from side to side, is smooth, and forms 

 part of the anterior wall of the pelvis. It gives attachment to the Levator ani, 

 Obturator internus, a few muscular fibres prolonged from the bladder, and the 

 pubo-prostatic ligaments. The upper border presents for examination a prominent 

 tubercle, which projects forward and is called the spine; to it are attached the 

 outer pillar of the external abdominal ring and Poupart's ligament. Passing 

 upward and outward from this is a prominent ridge, forming part of the ilio- 

 pectineal line, which marks the brim of the true pelvis: to it are attached a por- 

 tion of the conjoined tendon of the Internal oblique and Transversal is muscles, 

 Gimbernat's ligament, and the triangular fascia of the abdomen. Internal to the 

 spine of the os pubis is the crest, which extends from this process to the inner 

 extremity of the bone. It affords attachment, anteriorly, to the conjoined tendon 

 of the Internal oblique and Transversalis ; and posteriorly, to the Rectus and 

 Pyramidalis muscles. The point of junction of the crest with the inner border 

 of the bone is called the angle ; to it, as well as to the symphysis, is attached the 

 internal pillar of the external abdominal ring. The internal border is articular; 

 it is oval, covered by eight or nine transverse ridges, or a series of nipple-like 

 processes arranged in rows, separated by grooves ; they serve for the attachment 

 of a thin layer of cartilage, placed between it and the central fibro-cartilage. 

 The outer border presents a sharp margin, which forms part of the circumference 

 of the obturator foramen and affords attachment to the obturator membrane. 



The ascending or superior ramus extends from the body to the point of junc- 

 tion of the os pubis w r ith the ilium, and forms the upper part of the circumference 

 of the obturator foramen. It presents for examination a superior, inferior, and 

 posterior surface, and an outer extremity. The superior surface presents a con- 

 tinuation of the ilio-pectineal line, already mentioned as commencing at the pubic 

 spine. In front of this ridge the surface of bone is triangular in form, Avider 

 externally than internally, smooth, and is covered by the Pectineus muscle. 



