352 HUMAN ANATOMY. 



The motion which permits of separation takes place in the sacro-iliac joints, and 

 the pubic bones move downward as well as outward, adding materially to the 

 amount of pelvic space gained. With a separation of seven centimetres (two and 

 three-fourths inches), which is possible under gentle pressure without laceration of 

 the sacro-iliac ligaments, the gain in the conjugate diameter is 1.5 centimetres 

 (three-fifths of an inch). The projection of the anterior parietal boss into the pubic 

 interspace as the bones recede from each other adds to the space gained, so that by 

 opening the pubic joint to the extent of 6.5 centimetres (two and three-fifths inches) 

 the increase in the conjugate diameter amounts in effect to about two centimetres 

 (three-fourths of an inch) (Cameron). 



THE FEMUR. 



The femur, a typical long bone, has a shaft and two extremities. The lower 

 end rests on the tibia, pretty nearly in a horizontal plane ; from this the shaft slants 

 outward, forming an angle of about 10° with a vertical line. 



The upper extremity consists of a head, a 7ieck, and two trochanters. These 

 last are on the shaft at the junction with the neck, which runs upward and inward, 

 forming with it an angle of about 125° on the average. 



The head is a rounded swelling, representing rather more than half a sphere, 

 capping the end of the neck. It is not put on symmetrically, but covers more of 

 the upper side of the neck than of the lower, and probably, as a rule, more of the 

 front than of the back. Occasionally it is prolonged onto the upper anterior aspect 

 of the neck. It is smooth and covered with articular cartilage except at a depressioji 

 for the ligamentum teres, below and posterior to the axis of the head. Brockway,' 

 having examined 300 femurs, found this depression oval in 43 per cent. , with the 

 long axis running downward and somewhat backward, triangular in 35 per cent, 

 and circular in 22 per cent. In 84 per cent, he found vascular foramina, which are 

 larger in the young and not necessarily pervious in the old. In a few cases he found 

 a persistence of the foetal condition, — namely, a groove descending nearly to the 

 border of the articular surface. 



The neck* extends upward and inward, and usually forward. Being compressed 

 from before backward, it has a front and a back surface with thick upper and lower 

 borders. The lower rises more steeply from the shaft than the upper, so that the 

 neck is much broader at the base than where it joins the head. The lower border is 

 the longer, and the posterior surface is longer than the anterior. The neck is smooth 

 below and behind, rather rough in front and above. The upper border has numer- 

 ous nutrient foramina. The lower border, springing from the inner aspect of the 

 shaft, often presents a rounded ridge running to the lesser trochanter. The neck is 

 bounded behind by an elevation connecting the trochanters, the posterior intertro- 

 chanteric ridge. ^ The spiral line,^ also called the anterior intertrocha^iteric ridge, 

 bounds the greater part of the front. It starts at the little superior cervical tubercle, 

 at the junction of the top of the neck with the greater trochanter, runs downward and 

 inward to the level of the lesser trochanter, where it sometimes presents a smaller 

 inferior cervical tzibercle, and then, descending more rapidly, twists round the shaft 

 to join the inner lip of the linea aspera. Thus a small part of the neck between this 

 line and the lesser trochanter has no boundary. We have found the average length 

 of the neck on thirty-eight male bones and twenty-si.x female ones respectively 4.3 

 centimetres and 4 centimetres. Bertaux gives 46.6 millimetres and 4'* i millimetres 

 respectively. 



The greater trochanter' is a large process projecting upward and outward from 

 the top of the shaft and turning inward to overhang the back of the neck. Seen 

 from the outside its outline is roughly square, but the upper border generally rises 

 towards the back so as to form a point. The anterior surface presents a depressed 

 area for the insertion of the gluteus minimus. The outer side is crossed by a ridge 

 running downward and forward, to and in front of which is attached the gluteus 

 medius. The upper bo7'der receives at the front end the tendons of the obturator 

 internus and gemelli, and a little farther back that of the pyriformis. The hollow 

 ^ Proceedings of the Association of American Anatomists, 1896. 



^ Caput femoris. -Fovea capitis feraoris. ''Collura femoris. ''Crista intertroclianterica. ''Linea intertrochanterica. 

 ' Trochanter major. * 



