40 ANATOMY. 



loth Rib, has but one facet on its head. 



nth Rib, has no neck, no tuberosity, and but one facet on its head. 



I2th Rib, has neither neck, angle, tuberosity nor groove, and but one facet 



THE PELVIS. 



Describe the Pelvis. It is formed by the sacrum, coccyx, and two ossa 

 Innominata, and is divided into, \^LQ false pelvis, comprising the upper and 

 expanded portion, and the true pelvis, below the ilio-pectineal line. The 

 false pelvis corresponds to the iliac fossae, and is marked by its walls being 

 deficient anteriorly between the iliac borders, and posteriorly between the 

 sacrum and the posterior iliac spines. The true pelvis has a 



Brim, or inlet, bounded in front by the crest and spine of the pubes, benind 

 by the promontory of the sacrum, laterally by the ilio-pectineal line, its 

 axis corresponds to a line from the umbilicus to the middle of the coccyx. 

 Its average diameters in the female are, 4 inches antero-posteriorly, 4 over 

 5 inches transversely, 2 under 5 inches obliquely. 3 In the male each of 



these measurements is about 

 FlG - *9- y 2 an inch less. 



Cavity, is a short curved 

 canal, connecting the brim 

 with the outlet. In front its 

 depth is about ift inch, 

 posteriorly 4 to 4^, inches 

 in the female, 4^ to 5^ 

 inches in the male. Its 

 diameter is about 4^4" inches 

 in the female, 4^ inches in 

 the male, all around. 

 Outlet, is bounded by the pubic arch above, the tip of the coccyx behind, 

 and the tuberosities of the ischii laterally. Its axis, if prolonged, would 

 touch the promontory of the sacrum. Its diameters in the female are 

 each about 4*4' inches, in the male about 3^ inches. 

 State the chief differences between the male and female pelves. The male 

 pelvis is marked by strength of the bones, prominence of the muscular impres- 

 sions, a deep and narrow cavity, and large obturator foramina. The female pel- 

 vis has lighter bones, broader iliac fossae, the spines being further apart, greater 

 diameters at every point, the sacrum less curved, and the pubic arch wider. 



Describe the Sacrum. The " sacred bone " is triangular, curved, with its 

 convexity backwards, and is situated base upwards between the ossa innominata, 

 forming with the coccyx the posterior wall of the pelvis. The bone is formed 

 by the coalescence of 5 vertebrae, and presents the following points, viz 



