ANATOMY IN A NUTSHELL. 131 



it joins at a little less than half the distance between the body of the os pubis 

 and the tuberosity of the ischium. The Obturator externus, the Adductor 

 magnus and the Gracilis are attached to its outer surface. The Crus penis and 

 Transversus perinei are attached to its inner border. 



The cotyloid cavity, or acetabulum, is cup shaped. It looks outward, for- 

 ward and downward. The Ilium forms a little less than two-fifths of the aceta- 

 bulum. The os pubis forms a little more than one-fifth of the acetabulum. 

 The Ischium forms a little more than two-fifths of the acetabulum. The rim 

 of this cavity is prominent, but it is slightly lower in front and behind and has 

 a large notch below called the cotyloid notch. The depression in the center is 

 called the cotyloid fossa, around which is the articular portion of the cotyloid 

 cavity. 



The thyroid or obturator foramen — sometimes called foramen ovale is be- 

 low and internal to the acetabulum. This foramen is closed by a fibrous mem- 

 brane, leaving a space for the obturator groove in its upper margin. In the 

 male this foramen is nearly oval, while in the female it is more triangular. 



LESSON XXXIV. 



The Pelvis as a Whole. 



The word pelvis means basin. It is composed of four bones, the sacrum, 

 coccyx, and the two innominate. If we pass a plane through the sacral pro- 

 montory, ilio-pectineal line and the upper border of the symphysis, we divide 

 the pelvis into an upper or false pelvis and a lower or true pelvis. The upper 

 pelvis really belongs to the abdomen. The sacrum looks downward and for- 

 ward. Its anterior surface is broader than its posterior surface. It is held in 

 place by ligaments and the projections into the iliac articular surface. The 

 plane separating the true and false pelvis marks an angle of 60 degrees with the 

 horizontal. The plane of this outlet makes an angle of 16 degrees with the hor- 

 izontal. 



The base of the sacrum is about three and one-half inches above the upper 

 margin of the symphysis. The tip of the coccyx is one-half inch above the apex 

 of the subpubic arch. 



The ANTEROPOSTERIOR DIAMETER, CALLED THE CONJUGATE DIAMETER, LS 



measured from the sacro-vertebral angle to the symphysis. 



The transverse diameter represents the greatest width of the pelvic cav- 

 ity. 



The oblique diamkteh is measured from the sacro-iliac joint of one side 

 to the ilio-pectineal eminence of the other. 



The average measurements of the diameters of the pelvis in the 

 three planes are as follows: 



antero-posterior. oblique. i i; \\s\ i:nsK. 



Inlet 4 1-4 inches 5 inches 5 1-1 inches 



Cavity 4 3-4 inches •"> 1-4 inches 5 :^-4 inches 



Outlet . , .3 3-4 inches . ..4 1-2 inches 4 1-4 inches 



