196 THE SKELETON. 



Development. By three centres (Fig. 135) : one for the shaft, and one for 

 each extremity. Ossification commences in the centre of the shaft about the 

 seventh week, and gradually extends toward either extremity. The centre for 

 the upper epiphysis appears before or shortly after birth ; it is flattened in form, 

 and has a thin, tongue-shaped process in front which forms the tubercle. That 

 for the lower epiphysis appears in the second year. The lower epiphysis joins 

 the shaft at about the eighteenth, and the upper one about the twentieth, year. 

 Two additional centres occasionally exist one for the tongue-shaped process of the 

 upper epiphysis, which forms the tubercle, and one for the inner malleolus. 



Articulations. With three bones : the femur, fibula, and astragalus. 



Attachment of Muscles. To twelve: to the inner tuberosity, the Semimem- 

 branosus : to the outer tuberosity, the Tibialis anticus and Extensor longus digi- 

 torum and Biceps ; to the shaft, its internal surface, the Sartorius, Gracilis, and 

 Semitendinosus ; to its external surface, the Tibialis anticus; to its posterior sur- 

 face, the Popliteus, Soleus, Flexor longus digitorum, and Tibialis posticus ; to the 

 tubercle, the ligamentum patellae, by which the Quadriceps extensor muscle is 

 inserted into the tibia. In addition to these muscles, the Tensor fasciae femoris is 

 inserted indirectly into the tibia, through the ilio-tibial band, and the Peroneus 

 longus occasionally derives a few fibres of origin from the outer tuberosity. 



Surface Form. A considerable portion of the tibia is subcutaneous and easily to be felt. 

 At the upper extremity the tuberosities are to be recognized just below the knee. The internal 

 one is broad and smooth, and merges into the subcutaneous surface of the shaft below. The 

 external one is narrower and more prominent, and on it, about midway between the apex of the 

 patella and the head of the fibula, may be felt a prominent tubercle for the insertion of the ilio- 

 tibial band. In front of the upper end of the bone, between the tuberosities, is the tubercle of 

 the tibia, forming an oval eminence which is continuous below with the anterior border or crest 

 of the bone. This border can be felt, forming the prominence of the shin, in the upper two- 

 thirds of its extent as a sharp and flexuous ridge, curved outward above and inward below. In 

 the lower third of the leg the border disappears, and the bone is concealed by the tendons of 

 the muscles on the front of the leg. Internal to the anterior border is to be felt the broad 

 internal surface of the tibia, slightly encroached upon by the muscles in front and behind. It 

 commences above at the wide expanded inner tuberosity, and terminates below at the internal 

 malleolus. The internal malleolus is a broad prominence situated on a higher level and some- 

 what farther forward than the external malleolus. It overhangs the inner border of the arch 

 of the foot. Its anterior border is nearly straight ; its posterior border presents a sharp edge, 

 which forms the inner margin of the groove for the tendon of the Tibialis posticus muscle. 



The Fibula (Figs. 133, 134). 



The Fibula (fibula, a clasp) is situated at the outer side of the leg. It is the 

 smaller of the two bones, and, in proportion to its length, the most slender of all 

 the long bones ; it is placed on the outer side of the tibia, with which it is con- 

 nected above and below. Its upper extremity is small, placed toward the back of 

 the head of the tibia and below the level of the knee-joint, and excluded from its 

 formation; the lower extremity inclines a little forward, so as to be on a plane 

 anterior to that of the upper end, projects below the tibia, and forms the outer 

 ankle. It presents for examination a shaft and two extremities. 



The Upper Extremity, or Head, is of an irregular quadrate form, presenting 

 above a flattened articular facet, directed upward, forward, and inward, for artic- 

 ulation with a corresponding facet on the external tuberosity of the tibia. On 

 the outer side is a thick and rough prominence, continued behind into a pointed 

 eminence, the styloid process, which projects upward from the posterior part of 

 the head. The prominence gives attachment to the tendon of the Biceps muscle 

 and to the long external lateral ligament of the knee, the ligament dividing the 

 tendon into two parts. The summit of the styloid process gives attachment to the 

 short external lateral ligament. The remaining part of the circumference of the 

 head is rough, for the attachment of muscles and ligaments. It presents in front a 

 tubercle for the origin of the upper and anterior part of the Peroneus longus. and 

 the adjacent surface gives attachment to the anterior superior tibio-fibular ligament ; 

 and behind, another tubercle for the attachment of the posterior superior tibio- 

 h'bular ligament and the upper fibres of the Soleus muscle. 



