OSSIFICATION OF THE LOWER LIMB. 



Ill 



over the greater part of the ramus; a third, inconstant, is placed on the anterior inferior 

 spine of the ilium ; and a fourth, likewise inconstant, at the symphysis pubis. More- 

 over, between the extremities of the three principal osseous pieces, where they meet 

 in the acetabulum, there is situated in early life a thin stratum of cartilage, which 

 becomes ossified from one or more centres, and presents the shape of the letter Y. 



Fig. 102. 



Fig. 102. OSSIFICATION OF THE Os INNOMINATTJM. 



A, the condition of the bone at birth. Bone has spread from three nuclei into the 

 ilium, ischium, and pubis, which meet in the cartilage of the acetabulum. 



B, the bone of a child under six years of age. The rarni of the ischium and pubis are 

 farther ossified, but still separate. 



C, a bone of two or three years later, in which the rami are united. 



D, the bone of the right side from a person of about twenty years. Union has taken 

 place in the acetabulum, and the additional epiphyses are seen on the crest of the ilium, 

 the anterior inferior spine, the ischial tuberosity, and the margin of the symphysis pubis. 



In A, B and C, 1, ilium ; 2, ischium ; 3, pubis ; under D, 4, T-shaped piece formed of 

 several fragments which begin to ossify about the 14th year, and often unite into this 

 form before the completion of the acetabulum ; 5, epiphysis of the crest ; 6, that of the 

 tuberosity of the ischium ; 7, that of the symphysis pubis ; 8, that of the anterior inferior 

 spine of the ilium. 



The pelvis of the foetus and young child is of very small capacity proportionally 

 to the size of the body, and those viscera which are afterwards contained for the 

 most part in the true pelvis occupy a part of the abdominal cavity. The obliquity of 

 the pelvis is considerably greater in early life than in the adult. 



The/em?/?' is developed from one principal ossific centre for the shaft and from 

 four epiphyses, which appear in the following order : a single nucleus for the lower 

 extremity, one for the head, one for the great trochanter, and one for the small ; 

 these epiphyses become united to the main part of the bone in an order of time the 

 reverse of that in which they appear. 



The tibia and fibula each present, besides the principal centre of ossification for 

 the shaft, a superior and an inferior epiphysis. In the tibia the superior epiphysis 

 appears first, and it not only includes the lateral tuberosities, but sends down a pro- 

 cess in front, extending into the anterior tuberosity. In the fibula the inferior epi- 

 physis is the first to appear, and in both bones the inferior epiphyses are first united 

 to the shaft. 



The tarsal bones are ossified each from a single nucleus, with the exception of the 

 os calcis, which, in addition to its principal osseous centre, has an epiphysis incrusting 

 the upper part of its posterior extremity. 



The metatarsal bones and phalanges agree respectively with the corresponding 

 bones in the hand, in the mode of their development. Each bone is formed from a 

 principal piece and one epiphysis ; and while in the four outer metatarsal bones the 

 epiphysis is at the distal extremity, in the metatarsal bone of the great toe and in 

 the phalanges it is placed at the proximal extremity. 



