THE POSTERIOR LIMBS. 



101 



Fig. 64. 



deep groove in which passes a tendinous cord ; it is excavated, in front, by a 

 vertically elongated fossa which lodges the middle ligament of the patella. 

 The external tuberosity, medium in size and the most detached, has outwardly 

 an articular facet for the head of the fibula. The 

 internal tuberosity, the largest and least detached, 

 presents : on the sides, ligamentous imprints ; behind, 

 a small tubercle which gives attachment to the pos- 

 terior crucial ligament of the femoro-tibial articu- 

 lation. The superior face of the two lateral tube- 

 rosities is occupied by two Jarge irregular and 

 undulated articular surfaces, which respond to the 

 condyles of the femur through the medium of the 

 two meniscus- shaped fibro -cartilages interposed be- 

 tween the two bones. Of these two surfaces the 

 external is always the widest, because it serves, by 

 its posterior part, for the gliding movements of the 

 popliteal tendon. They are separated from each 

 other by the tibial spine, a conical articular eminence 

 divided into two lateral parts by a groove of inser- 

 tion excavated at its base, and in front by two lateral 

 facets for the insertion, anteriorly, of the two inter- 

 articular cartilages ; it is bordered behind by another 

 fossa which receives the posterior insertion of the 

 internal meniscus. 



The inferior extremity, flattened behind and before, 

 exhibits an articular surface moulded on the pulley 

 of the astragalus, and two lateral tuberosities. The 

 articular surface is formed by two deep cavities oblique 

 from behind to before and within outwards, and 

 separated by a median tenon which terminates pos- 

 teriorly by a very prominent projection on which thq 

 bone rests when it is made to stand vertically on 

 a horizontal plane. The external tuberosity 1 projects 

 but little, and is traversed in its middle by a vertical 

 fissure. The internal tuberosity, 2 better defined, is 

 margined posteriorly by an oblique channel. 



Structure and development. The tibia is very 

 compact in its inferior portion, and is developed from 

 four chief centres of ossification. The body is formed 

 by one and the superior extremity by two, the anterior 

 tuberosity taking one of these ; the last develops the 

 whole of the inferior extremity. It is rare to see 

 the external tuberosity of this extremity formed from 

 a separate nucleus. 



2. Fibula (or Peroneus). 



^ A small, undeveloped bone, elongated and sty- 

 loid in shape, situated outside the tibia, and extend- 

 ing from the superior extremity of that bone to the 

 middle or lower third of its body. 



The middle portion of the fibula is thin and cylin- 

 drical, and forms above, in common with the external border of the larger 

 1 The external malleolus of Man. 2 The internal malleolus. 



10 



POSTERIOR VIEW OF 

 RIGHT TIBIA. 



Tibial spine; 2, Fossa 

 for the insertion of the 

 internal meniscus ; 3, 

 External tuberosity with 

 articulation for the fib- 

 ula; 4, Fossa for the 

 insertion of external 

 meniscus ; 5, Fibula, 

 forming with the tibia 

 the tibial arch; 6, Shaft, 

 or body of the tibia; 

 7, 8, External and in- 

 ternal malleoli, inferior 

 tuberosities, or lateral 

 processes of the tibia ; 

 9, Articular trochlese 

 with a median ridge, 

 for articulation with the 

 astragalus. 



