192 



HEALTH AND DISEASE 



are the thicker and stronger. They increase in length from before back- 

 ward to the eleventh, after which they become shorter. 



The Pelvis (figs. 294, 295). The bony pelvis or hip girdle consists 

 of two portions, termed coxae or ossa innominata, which, together with 

 the sacrum and the front segments of the tail-bones, form the cavity of 

 the pelvis. 



The ossa innominata are flat, irregular bones, which, after forming the 

 sides of the pelvic cavity, join together below to form its floor. In the 

 foetus each innominate bone consists of three pieces, termed the ilium, the 



ischium, and the 

 pubis. The ilium, 

 the largest of the 

 three, is that portion 

 which unites with the 

 sacrum above, with 

 the acetabulum or 

 femoral joint below, 

 and outwardly forms 

 the " point of the 

 hip ". The ischium 

 is that portion which, 

 on leaving the hip- 

 joint, which it assists 

 in forming, passes 

 backward to the point 

 of the buttock, and 

 inward to join its 

 fellow on the opposite 

 side, thus contribut- 

 ing to the floor of the 

 pelvis, and to the for- 

 mation of a large opening there the obturator foramen. 



The pubis is the smallest of the three bones entering into the forma- 

 tion of the coxa. It is situated in front of the floor of the pelvis, 

 which, together with the foramen just referred to, it concurs in forming. 

 With the ilium and ischium it also joins in making up the acetabulum 

 or cup-like cavity into which the head of the femur fits to form the 

 nip-joint. 



The two pubic bones unite on the floor of the pelvis to form a seam, 

 or, as it is termed, the symphysis pubis. 



The cavity of the pelvis is much larger at the front or inlet than at 



Fig. 295. Pelvis and Sacrum (Inferior Aspect) 



i Anterior Articular Body of Sacrum. 2 Posterior Spinous Process of Ilium. 



* Crista of Ilium. 4 Anterior Spinous Process of Ilium. 5 Neck of Ilium. 



* Acetabulum. 7 Obturator Foramen. 8 Lateral Ischiatic Notch. 9 Ischiatic 

 Arch. 10 Tuberosity of Ischium. " Coccygeal Extremity of Sacrum. 12 Sub- 

 sacral Foramina. " Anterior Articular Process of Sacrum. 



