PELVIS. 155 



cartilaginous. At about the sixth year, the rami of the pubes and ischium are 

 almost completely ossified. About the thirteenth or fourteenth year, the three 

 divisions of the bone have extended their growth into the bottom of the acetabu- 

 lum, being separated from each other by a Y-shaped portion of cartilage, which 

 now presents traces of ossification. The ilium and ischium then become joined, 

 and lastly the pubes, through the intervention of the portion above-mentioned. 

 At about the age of puberty, ossification takes place in each of the remaining 

 portions, and they become joined to the rest of the bone about the twenty-fifth 

 year. 



Articulations. With its fellow of the opposite side, the sacrum and femur. 



Attachment of Muscles. Ilium. To the outer lip of the crest, the Tensor 

 vaginae femoris, Obliquus externus abdominis, and Latissimus dorsi; to the internal 

 lip, the Transversalis, Quadratus lumborum, and Erector spinad ; to the interspace 

 between the lips, the Obliquus internus. To the outer surface of the ilium, the 

 Gluteus maximus, Gluteus medius, Gluteus minimus, reflected tendon of Kectus, 

 portion of Pyriformis ; to the internal surface, the Iliacus ; to the anterior border, 

 the Sartorius and straight tendon of the Eectus. Ischium. To its outer surface, 

 the Obturator externus; internal surface, Obturator internus and Levator ani. 

 To the spine, the Gemellus superior, Levator ani, and Coccygeus. To the 

 tuberosity, the Biceps, Semi-tendinosus, Semi-membranosus, Quadratus femoris, 

 Adductor magnus, Gemellus inferior, Transversus perinasi, Erector penis. Pubes, 

 the Obliquus externus, Obliquus internus, Transversalis, Eectus, Pyramidalis, 

 Psoas parvus, Pectineus, Adductor longus, Adductor brevis, Gracilis, Obtu- 

 rator externus and internus, Levator ani, Compressor urethrae, and occasionally a 

 few fibres of the Accelerator urinae. 



THE PELVIS (figs. 100 and 101). 



The pelvis, so called from its resemblance to a basin (*Xi>!), is stronger and 

 more massively constructed than either of the other osseous cavities already con- 

 sidered ; it is a bony ring, interposed between the lower end of the spine, which 

 it supports, and the lower extremities, upon which it rests. It is composed of 

 four bones the two ossa innominata, which bound it on either side and in front ; 

 and the sacrum and coccyx, which complete it behind. 



The pelvis is divided by a prominent line, the linea ilio-pectinea, into a false 

 and true pelvis. 



The false pelvis is all that expanded portion of the pelvic cavity which is 

 situated above the linea ilio-pectinea. It is bounded on each side by the ossa ilii ; 

 in front it is incomplete, presenting a wide interval between the spinous processes 

 of the ilia on either side, filled up in the recent state by the parietes of the 

 abdomen ; behind, in the middle line, is a deep notch. This broad shallow cavity 

 is admirably adapted to support the intestines, and to transmit part of their weight 

 to the anterior wall of the abdomen. 



The true pelvis is all that part of the pelvic cavity which is situated beneath 

 the linea ilio-pectinea. It is smaller than the false pelvis, but its walls are more 

 perfect. For convenience of description, it may be divided into a superior cir- 

 cumference or inlet, an inferior circumference or outlet, and a cavity. 



The superior circumference forms the margin or brim of the pelvis, the included 

 space being called the inlet. It is formed by the linea ilio-pectinea, completed 

 in front by the spine and crest of the pubes, and behind by the anterior margin of 

 the base of the sacrum and sacro-vertebral angle. 



The inlet of the pelvis is somewhat heart-shaped, obtusely pointed in front, 

 diverging on either side, and encroached upon behind by the projection forwards 

 of the promontory of the sacrum. It has three principal diameters: antero- 

 posterior or sacro-pubic, transverse, and oblique. The antero-posterior extends 

 from the sacro-vertebral angle to the symphysis pubis ; its average measurement 

 is four inches. The transverse extends across the greatest width of the inlet, 



