20 BONES OF THE TRUNK. 



Ischium. — This is the most inferior part of "the innominatum. It 

 consists of a body and branch ; the external surface of the body'' is 

 rough ; the internal surface is smooth, and is called the plane of the 

 ischium. The posterior border presents a projection called the spine, 

 into which is inserted the lesser sacro-sciatic ligament, and beneath 

 the spine is a groove in which plays the tendon of the obturator in- 

 ternus muscle. The inferior portion of the body is called the tuber- 

 osity,'^ from which arise the ^emi-membranosus, semi-tendinosus, bi- 

 ceps, and adductor muscles; in front there is a ridge into which is 

 inserted the greater sacro-sciatic ligament. 



The ramus or branch is short and thick, and ascends forward 

 and inward, joining the ramus of the pubes, and forming a portion 

 of the pubic arch ;" externally it is rough, and internally it is 

 smooth, whence arises the crus of the penis. 



Pubes. — It forms the anterior boundary of the pelvis," and con- 

 sists of a body and descending ramus or branch. 



The body articulates with its fellow by a vertical surface,^ called 

 the symphysis. The superior portion of the body at right angles 

 with the symphysis is horizo7ital^ and limited externally by a pro- 

 jection' called the spinous process ; from this process there divei'ge 

 two ridges ; the posterior,'' is called the crista of the pubes, or linea 

 pectinea, and to it is attached a portion of Poupart's ligament ; the 

 anterior is sometimes called linea innominata. Between these ridges 

 is included a triangular space," the base being the ilio-pectineal emi- 

 nence," and the apex the spinous process; from this space arises the 

 pectineus muscle, and over it pass the femoral vessels. 



The ramus descends to join that of the ischium, and form a part 

 of the pelvic arch; externally it is rough for the origin of ihe ab- 

 ductor muscles; infernally it is smooth, and from it arises the crus 

 of the penis. 



The acetabuhim,^ is a deep hemispherical concavity upon the outer 

 side of the bone for the articulation of the head of the femur. The 

 brim of this cavity is notched on the lower edge. In the bottom of 

 the cavity is a rough depression occupied by a mass of fat, commonly 

 called a gland of Havers. Immediately beneath the acetabulum is 

 a groove, in which plays the tendon of the external obturator muscle. 



The obturator 01 thyroid foramen, \s that large opening in the 

 front and lower part of the bone, which is filled up by a mem- 

 branous ligament, with the exception of a groove at its upper part, 

 through which pass the obturator vessels and nerve. Its shape is 

 oval, but rather triangular in males. 



THORAX. 



This cavity is formed by the dorsal vertebnie, ribs, and sternum ; 

 its figure is conoidal, flattened in front, and concave behind ; the 



