72 ELEMENTARY BIOLOGY. [CHAP. 



in position and furnishing the middle third of 

 the acetabulum. 



yS. An anterior elongated piece (/7/V/;;/); subcylindri- 

 cal in front, behind, laterally compressed {crista 

 ilii) ; it furnishes rather more than the anterior 

 third of the acetabulum. Its articulation with the 

 sacrum is effected through the agency of a car- 

 tilaginous supra-ilium ; related to the ilium, as is 

 the supra-scapula to the scapula in the shoulder- 

 girdle (cf. p. 69). 



y. A posterior, laterally compressed piece {iscJiium') ; 

 united with its fellow in the middle line. It 

 meets the ilium above, below it is separated 

 from it by the pubis ; it furnishes rather less 

 than the posterior third of the acetabulum. 



The skeleton of the hind limb. 



a. The thigh-bone (os fcmoris) ; its cylindrical shaft 

 and rounded articular ends. 



if. I'he leg-bone {os cruris). 



a. A long cylindrical bone, expanded at its articular 

 extremities. Its upper end; excavated for ar- 

 ticulation upon the femur. Its lower end; 

 rounded and notched to give passage to the 

 tendon of the tibialis posticus muscle (Sect. H. 

 7. a. /?.). 



13. The longitudinal grooves on it ; indicating that 

 it is really made up of two united bones, the 

 tibia and the Jibn/a. 



y. The iiutritive foramen (for passage of nen-es and 

 blood-vessels into its interior) ; a small slit-like 

 perforation of the middle of the shaft. 



