TARSUS. 



249 



JJnitet about 208 y? 



At 'about the middle of this surface is the nutrient foramen, which is directed 

 downwards. 



In order to distinguish the side to which Fig. 179. Plan of the Development 

 the bone belongs, hold it with the lower ex- of the Fibula. By Three Centres, 

 tremity downwards, and the broad groove for 

 the Peronei tendons backwards, towards the 

 holder; the triangular subcutaneous surface 

 will then be directed to the side to which the 

 bone belongs. 



Articulations. With two bones; the tibia 

 and astragalus. 



Development. By three centres (Fig. 179); 

 one for the shaft, and one for each extremity. 

 Ossification commences in the shaft about the 

 sixth week of fostal life, a little later than in 

 the tibia, and extends gradually towards the 

 extremities. At birth both ends are cartila- 

 ginous. Ossification commences in the lower 

 end in the second year, and in the upper one 

 about the fourth year. The lower epiphysis, 

 the first in which ossification commences, be- 

 comes united to the shaft first, contrary to the 

 law which appears to prevail with regard to 

 the junction of the epiphyses with the shaft; 

 this takes place about the twentieth year ; the 

 upper epiphysis is joined about the twenty-fifth 

 year. 1 



Attachment of Muscles. To the head, the Bi- 

 ceps, Soleus, and Peroneus Longus; to the 

 shaft, its anterior surface, the Extensor Longus Digitorum, Peroneus Tertius, 

 and Extensor Longus Pollicis; to the internal surface, the Soleus, Tibialis 

 Posticus, and Flexor Longus Pollicis; to the external surface, the Peroneus 

 Longus and Peroneus Brevis. 



The Skeleton of the Foot (Figs. 180, 181) consists of three divisions : the 

 Tarsus, Metatarsus, and Phalanges. 



THE TARSUS. 



The bones of the Tarsus are seven in number, viz., the calcaneum, or os 

 calcis, astragalus, cuboid, scaphoid, internal, middle, and external cuneiform 

 bones. 



THE Os CALCIS. 



The Calcaneum, or Os Calcis, is the largest and strongest of the tarsal bones. 

 It is irregularly cuboidal in form, and situated at the lower and back part of the 

 foot, serving to transmit the weight of the body to the ground, and forming a 

 strong lever for the muscles of the calf. It presents for examination six sur- 

 faces : superior, inferior, external, internal, anterior, and posterior. 



The superior surface is formed behind, of the upper aspect of that part of the 

 os calcis which projects backwards to form the heel. It varies in length in 

 different individuals ; is convex from side to side, concave from before back- 

 wards, and corresponds above to a mass of adipose substance placed in front of 

 the tendo Achillis. In the middle of the superior surface are two (sometimes 

 three) articular facets, separated by a broad shallow groove, which is directed 



1 It will be observed that in the fibula, as in other long bones, the epiphysis, towards which 

 the nutrient artery is directed, is the one first joined to the shaft. 



