=The Tibia.=--The tibia or _shin bone_ is next longest to the femur and is on the inner side of the leg, corresponding to the ulna in the arm. The _shaft_ is prismoid and is more slender for the lower quarter, where fracture is consequently most frequent. The anterior border forms the _crest_ or shin and can be felt for its upper two-thirds. The lower extremity, which is smaller than the upper, articulates with the astragalus bone of the ankle and with the fibula. Its _head_ or upper extremity is expanded into two lateral _tuberositis_ for articulation with the femur and for muscular attachment, both of which can easily be felt just below the bend of the knee. Their upper surfaces are smooth and concave, with a vertical bifid spine in the middle and a prominent tubercle for the attachment of the semilunar cartilages on either side. On the anterior surface of the head, below, is a rough eminence or tubercle, which also can be felt. The lower part of this is for the attachment of the ligamentum patellæ, while the upper part, which is smoother, is for the bursa that is placed under the tendon to prevent friction. On the back of the outer tuberosity is a facet for the head of the fibula. At the lower end there projects downward on the inner side, overhanging the arch of the foot, the _internal malleolus_, the prominent part of the ankle. It is on a higher level and somewhat farther forward than the _external malleolus_. =The Fibula.=--The fibula is the most slender of all the bones in proportion to its length and is on the outer side of the leg. Its _head_ is small and placed toward the back of the tibia below the knee-joint, from which it is excluded. The head articulates with the external tuberosity and has extending upward from it the styloid process. To it is attached the _biceps tendon_ or _outer hamstring_. At the lower extremity of the shaft is the _external malleolus_, which articulates with the astragalus and forms the outer ankle. The only parts of the fibula that can be felt, besides the malleolus, which is very prominent, are the head and the lower external surface of the shaft. In _fracture of the leg_ both bones are usually broken, though either may be broken separately. _Pott’s fracture_ is fracture of the lower fibula, and may be caused by stamping hard when stepping on to the sidewalk. In rickets the tibia becomes bowed outward and forward, causing _bow leg_, a condition which in very young children may be rectified by manipulation. Later on braces are needed and after five years the bones have to be broken and set straight.