254 



OSTEOLOGY. 



Appears about 

 3-4 years 



tibia than in the adult. Its extremities are cartilaginous, the distal extremity not being 

 as long as the medial malleolar cartilage of the tibia. It is in this, however, that an 

 ossific centre first appears about the end of the second year, which increases rapidly 

 in size, and unites with the body in about nineteen years. The centre for the proximal 

 epiphysis begins to ossify about the third or fourth year, and union with the body is 

 not complete until a period somewhat later than that for the distal epiphysis. The mode 



of ossification of the distal extremity is an 



Fuses with shaft , . ,-, -, -. , , . . , 



about 20-24 years exception to the general rule that epiphyses 

 which are the first to ossify are the last to unite 

 with the body. This may possibly be accounted 

 for by the fact that the distal end is functionally more 

 important than the rudimentary proximal end, since in 

 man alone, of all vertebrates, does the lateral malleolus 

 reach beyond the level of the medial malleolus. Its 

 early union with the body is doubtless required to 

 ensure the stability of the ankle-joint necessitated 

 by the assumption of the erect position. 



In its earlier stages of development it has been stated, 

 on the authority of Leboucq, Gegenbaur, and others, that 

 the fibula as well as the tibia is in contact with the femur. 

 This is, however, denied by Grunbaum (" Proc. Anat Soc.," 

 Journ. Anat. and PhysioL, vol. xxvi. p. 22), who states that 

 after the sixth week the fibula is not in contact with the 

 femur, and that prior to that date it is impossible to 

 differentiate the tissue which is to form femur from that 

 which forms fibula. 



Appears about 

 2nd year 



Fuses with shaft 

 about 19 years 



At About About 



birth. 12 years. 16 years. 



FIG. 253. OSSIFICATION OF FIBULA. 



BONES OF THE FOOT. 



The bones of the foot, twenty-six in number, are arranged 

 in three groups : the tarsal, seven in number ; the rneta- 

 tarsal, five in number ; the phalanges, fourteen in number. 

 Comparing the foot with the hand, the student will be 

 struck with the great proportionate size of the tarsus as compared with the carpus, and the 

 reduction in size of the bones of the toes as compared with the fingers. The size of the meta- 

 tarsal segment more nearly equals that of the metacarpus. 



The Tarsus. 



The tarsus consists of seven bones (ossa tarsi) the talus or astragalus, 

 calcaneus, navicular or scaphoid, three cuneiforms, and the cuboid. Of irregular 

 form and varying size, they may be described as roughly cubical, presenting for 

 examination dorsal and plantar surfaces, as well as anterior, posterior, medial, 

 and lateral aspects. 



The Talus. 



The talus (O.T. astragalus) is the bone through which the body weight is 

 transmitted from the leg to the foot. Proximally the tibia rests upon it, whilst 

 on either side it articulates with the medial and lateral malleolar processes of the 

 tibia and fibula respectively ; inferiorly it overlies the calcaneus, and anteriorly it 

 articulates with the navicular. For descriptive purposes the bone is divisible into 

 three parts the corpus tali (body) blended in front with the collum tali (neck), 

 which supports the caput tali (head). 



The dorsal surface of the body is provided with a saddle-shaped articular 

 surface (trochlea tali), broader in front than behind, for articulation with the distal 

 surface of the tibia. The medial edge of the trochlea is straight ; whilst the lateral 

 border, which is sharp in front and more rounded behind, is curved medially pos- 

 teriorly, where it is bevelled to form a narrow, elongated, triangular facet, which 

 is in contact with the transverse or distal tibio-fibular ligament during flexion of 

 the ankle. (Fawcett, Ed. Med. Journ., 1895.) Over the lateral border the cartilage- 

 covered surface is continuous laterally with an extensive area of the form of a 

 quadrant. This is concave from above downwards, and articulates with the medial 



