THE BONES OF THE LOWER LIMB 



*49 



Posteriorly is the groove for the tendons of the tibialis posticus and 

 flexor longus digitorum. The outer aspect of the lower extremity 

 presents a concave facet for the fibula, cind above this a concave 

 triangular rough sin-face about i^ inches long for the inferior inter- 

 osseous ligament. 



The inferior extremity of the tibia presents many nutrient 

 foramina for branches of the anterior and posterior tibial, internal 

 malleolar, and anterior peroneal, arteries. 



Articulations. — Superiorly with the condyles of the femur above, 

 and the head of the fibula postero-extemally, and inferiorly with 

 the fibula externally, and the superior and intemaJ aspects of 

 the astragalus below. 



Structure. — The structure is that of a long bone. The medullary 

 canal extends above to a point about i^ inches below the lower 

 margin of the anterior tuberosity, and inferiorly to a point about 

 I inch below the lower extremity of the crest. The cancellated 

 tissue of the upper epiphysis has its lamellae disposed somewhat 

 vertically, whilst that of the upper end of the shaft has its lamellae 

 arranged in the form of arches. In the lower part of the shaft the 

 cancellous lamella; are disposed vertically, and the cancellated 

 tissue of the lower epiphysis is closely meshed. 



Varieties. — (i) The tibia is sometimes much compressed laterally, which leads 

 to an increase in its antero-posterior diameter. In these cases the vertical 

 ridge posteriorly becomes unduly promi- 

 nent, a condition which is associated 

 with a large development of the tibialis 

 posticus muscle. Such a bone is spoken of 

 cis being platycnemic (broad -legged), and 

 the condition is known as platycnemism 

 (broadness of tibia). (2) The anterior 

 aspect of the lower extremity of the bone 

 sometimes presents a pressure facet at its 

 outer part for articulation with the upper 

 surface of the neck of the astragalus in 

 extreme flexion of the ankle-joint. 



Ossification. — The tibia is ossified in 

 cartilage from i primary and 3 secondary 

 centres. 



The primary centre appears at the 

 centre of the shaft about the jth week. 

 The 3 secondary centres are disposed as 

 follows: 2 are superior, one for the head, 

 and the other for the tubercle ; and i is 

 inferior for the lower extremity and inter- 

 nal malleolus. Upper Extremity. — The 

 centre for the head appears just before 

 birth, and from it the external and in- 

 ternal tuberosities are ossified, which constitute the superior epiphysis. The 

 centre lor the tubercle appears about the 12th year. Soon afterwards it joins 

 the superior epiphysis, which unites with the shaft about the 22nd year. In 

 some cases the tubercle is entirely ossified from the centre for the head. In 

 other cases th;; upper smooth part of the tubercle is ossified from the centre 

 for the head, and the lower rough part derives its ossification from the primar}' 

 centre for the shaft. Lower Extremity. — ^The centre for the lower ex- 

 tremity and internal malleolus appears towards the end of the 2>Mf year, and 

 this lower epiphysis joins about the iSth year. 



Appears just liefore birtb, and 



joins about 22 

 May appear about the 12th year, 

 and joins soon thereafter 



Appears in the 7th week 

 (intra-uterine) 



Fig. 



;;^_ Appears at end of 2nd year, 

 and joins about 18. 



146. — Ossification of the 

 Tibia. 



