166 ANATOMY IN A NUTSHELL. 



LESSON XL1Y. 



The Tibia. 



The word tibia means flute. It is also called the shin bone and is situated 

 on a plane anterior to and on the inner side of the fibula. It articulates with the 

 lemur above, tin 1 astragalus below, and the fibula externally. It sustains the 

 uri'Jn of the entire body above the knee-joint as the fibula does not enter into 

 this articulation. 



The superior expanded portion is called the head, each side of which is a 

 tuberosity. These tuberosities are continuous in front but are separated be- 

 hind by the popliteal notch. The upper surface of each tuberosity is concave 

 to receive the condyles of the femur. 



The internal tuberosity is larger than the external one, and its articular 

 surface is more concave and Longer. A horizontal groove for the Semimem- 

 branosus muscle is behind this articular surface close to its inner border. 



The external tuberosity gives attachment to the ilio-tibial band at the junc- 

 tion of the anterior and outer surfaces, at which place there is a prominent tuber- 

 cle. The Extensor Longus digitorum and the Biceps have a \'v\\ fibers of at- 

 tachment immediately below and in front. The fibula articulates with the 

 posterior and under part in a flat facet which looks downward, outward, and 

 backward. The articular surface of this tuberosity is concave from side to side, 

 but convex from before backward, and its circumference is almost circular. 

 The semilunar fibro-cartilages are situated around the circumference of each 

 of these articular surfaces where they are flattened. 



The spine is an elevation between these articular surfaces. The summit of 

 the spine has two tubercles with an intervening space. The depressions in 

 iVi .lit and behind the spine are for the attachment of the crucial ligaments. 

 This posterior depression is continuous into the popliteal notch, which separates 

 the tuberosities posteriorly. The anterior tuberosity or tubercle is at the junc- 

 tion of the head and the -haft anteriorly. The lower half of this tubercle gives 

 attachment to the ligamentum patellae. 



The shaft which is triangular on cross section is smallest at the junction of 

 the upper two-thirds with the lower one-third. It has three borders and three 

 surfaces. The anterior border separates the internal and external surfaces and 

 extends from the anterior tuberosity or tubercle to the front of the inner mal- 

 leolus. The crest of the tibia i> the upper two-thirds of this border. The lower 

 one-third of this border is smooth. The internal border separates the internal 

 and posterior surfaces. It commences above at the back of the inner tuberosity 

 and extends below to the posterior border of the internal malleolus. This 

 border ie rnos1 distind in the middle third of the bone. The external border, 

 also called interosseous ridge, separate- the external and posterior surfaces. It 

 gives attachment to the interosseous membrane and is thin and sharp in its 

 middle portion. 



The internal surface is nearly subcutaneous and is convex. The insertion 



