198 



THE SKELETON. 



Upper extremity. 



convex from above downward, which articulates with a corresponding surface on 

 the outer side of the astragalus. Behind and beneath the articular surface is a 

 rough depression which gives attachment to the posterior fasciculus of the external 

 lateral ligament of the ankle. The anterior border is thick and rough, and marked 

 below by a depression for the attachment of the anterior fasciculus of the external 

 lateral ligament. The posterior border is broad and marked by a shallow groove, 

 for the passage of the tendons of the Peroneus longus and brevis muscles. The 

 summit is rounded, and gives attachment to the middle fasciculus of the external 

 lateral ligament. 



In order to distinguish the side to which the bone belongs, hold it with the 

 lower extremity downward and the broad groove for the Peronei tendons back- 

 ward i, e , toward 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. 136) : one for the shaft, and one for 

 each extremity. Ossification commences in the shaft about the eighth week of 

 foetal life, a little later than in the tibia, and extends gradually toward the 

 extremities. At birth both ends are cartilaginous. 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, becomes united to 

 the shaft about the twentieth year; the upper epiphysis joins about the twenty- 

 fifth year. Ossification appearing first in the lower epiphysis is contrary to the 

 rule which prevails with regard to the commencement of ossification in epiphyses 

 viz. that that epiphysis toward which the nutrient artery is directed commences 

 to ossify last ; but it follows the rule which prevails with regard to the union of 

 epiphyses, by uniting first. 



Attachment of Muscles. To nine : to the head, 

 the Biceps, Soleus, and Peroneus longus ; to the 

 shaft, its anterior surface,- the Extensor longus digi- 

 torum, Peroneus tertius, and Extensor proprius 

 hallucis ; to the internal surface, the Tibialis pos- 

 ticus ; to the posterior surface, the Soleus and Flexor 

 longus haliucis ; to the external surface, the Peroneus 

 longus and brevis. 



Surface Form. The only parts of the fibula which are 

 to be felt are the head and the lower part of the external sur- 

 face of the shaft and the external malleolus. The head is to 

 be seen and felt behind and to the outer side of the outer 

 tuberosity of the tibia. It presents a small, prominent 

 triangular^ eminence slightly above the level of the tubercle 

 of the tibia. The external malleolus presents a narrow elon- 

 gated prominence, situated on a plane posterior to the internal 

 malleolus and reaching to a lower level. From it may be 

 traced the lower third or half of the external surface of the 

 shaft of the bone in the interval between the Peroneus tertius 

 in front and the other two Peronei tendons behind. 



Surgical Anatomy. In fractures of the bones of the 

 leg both bones are usually fractured, but each bone may be 

 broken separately, the fibula more frequently than the tibia. 

 Fracture of both bones may be caused eitner by direct or indirect 

 violence. When it occurs from indirect force, the fracture in 

 the tibia is at the junction of the middle and lower third of 

 the bone. Many causes conduce to render this the weakest 

 part of the bone. The fracture of the fibula is usually at 

 rather a higher level. These fractures present great variety, 

 both as regards their direction and condition. They may be 

 oblique, transverse, longitudinal, or spiral. When' oblique, 

 they are usually the result of indirect violence, and the direction of the fracture is from behind, 

 downward, forward, and inward in many cases, but may be downward and outward or downward 

 and backwcard. When transverse, the fracture is often at the upper part of the bone, and is the 

 result of direct violence. The spiral fracture usually commences as a vertical fissure, involving 

 the ankle-joint, ana is associated with fracture of the fibula higher up. It is the result of torsion, 

 from twisting of the body whilst the foot is fixed. 



Appears about^ 

 4th year. 



Appears at 

 2nd year. 



Unites about 

 25th year. 



Unites about 

 20th year. 



Lower extremity. 



FIG. 136. Plan of the develop- 

 ment of the fibula. By three centres. 



