296 



THE SKELETON. 



Upper extremity. 



Appears at 

 birth. 



.Joins shaft about 

 20th year. 



the attachment of the anterior ligament of the ankle-joint ; the posterior surface 

 presents a superficial groove directed obliquely downward and inward, continuous 

 with a similar groove on the posterior extremity of the astragalus, and serving 

 for the passage of the tendon of the Flexor longus hallucis ; the external surface 

 presents a triangular rough depression for the attachment of the inferior inter- 

 osseous ligament connecting it with the fibula ; the lower part of this depression 

 is smooth, covered with cartilage in the recent state, and articulates with the 

 fibula. This surface is bounded by two prominent ridges, continuous above with 

 the interosseous ridge ; they afford attachment to the anterior and posterior infe- 

 rior tibio-fibular ligaments. The internal surface of the lower extremity is pro- 

 longed downward to form a strong pyramidal process, flattened from without 

 inward the inner malleolus. The inner surface of this process is convex and sub- 

 cutaneous ; its outer surface is smooth and slightly concave, and articulates with 

 the astragalus ; its anterior border is rough, for the attachment of the anterior 

 fibres of the Deltoid ligament ; its posterior border presents a broad and deep 

 groove, directed obliquely downward and inward, which is occasionally double : 

 this groove transmits the tendons of the Tibialis posticus and Flexor longus digi- 

 torum muscles. The summit of the internal malleolus is marked by a rough 

 depression behind, for the attachment of the internal lateral ligament of the 

 ankle-joint. 



Structure. Like that of the other long bones. At the junction of the middle 



and lower third, where the bone is smallest, the wall .of the shaft is thicker than 



in other parts, in order to compensate for the smallness of the calibre of the bone. 



Development. By three centres (Fig. 222) : one for the shaft, and one for 



each extremity. Ossification commences 

 in the centre of the shaft about the 

 seventh week, and gradually extends to- 

 ward either extremity. The centre for 

 the upper epiphysis appears during the 

 first year; 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 inter- 

 nal 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. 



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 ilic- 



Appears at 2nd_ 

 year. 



Joins shaft about 

 18th year. 



Lower extremity 



FIG. 222. Plan of the development of the tibia. 

 By three centres. 



