226 OSTEOLOGY. 
and covered by a bursa, while the lower part is rough and serves for the attach- 
ment of the hgamentum patellee. 
Considered in its entirety, the upper extremity of the tibia is broader trans- 
versely than antero-posteriorly, and is inclined backwards so as to overhang the 
shaft posteriorly. 
The shaft (corpus tibiz) is irregularly three-sided. It is narrowest about the 
junction of its middle and lower thirds, and expands above and below to support 
the extremities. Running down the front of the bone, there is a gently-curved 
prominent margin confluent above with the tubercle, but fading away inferiorly on 
the anterior surface of the lower third of the bone, where it may be traced in the 
direction of the anterior border of the internal malleolus. This is the crest or shin 
(crista anterior), which is subcutaneous throughout its entire length. To the 
inner side of this is a smooth, shghtly convex surface, which reaches as high as the 
internal tuberosity above, and inferiorly becomes continuous with the inner surface 
of the internal malleolus. This*is the internal or subcutaneous surface (facies 
medialis) of the shaft, which is covered only by skin and superficial fascia, except 
in its upper fourth, where the tendons of the sartorius, eracilis, and semitendinosus 
muscles overle it, as they pass towards their insertions. This surface is limited 
posteriorly by the internal border (margo medialis) which passes from the inner and 
under surface of the internal tuberosity above to the hinder border of the internal 
malleolus below. This border is rounded and indefinite above and below, being 
usually best marked about its middle third. To the outer side of the tibial crest is the 
external surface of the bone (facies lateralis) ; it is hmited behind by a straight vertical 
ridge, the crista interossea, to which the interosseous membrane, which occupies the 
interval between the tibia and the fibula, is attached. This ridge commences above, 
near the middle of the outer and under surface of the external tuberosity, and 
terminates below about two inches above the lower extremity by dividing into two 
lines, which separate and enclose between them the surface for articulation with 
the lower end of the fibula, and the area of attachment of the inferior interosseous 
ligament, which here unites the two bones. In its upper two-thirds the external 
surface provides an extensive origin for the tibialis anticus. Inferiorly, where the 
tibial crest is no longer well defined, the external surface turns forward on to the 
front of the shaft, and is limited inferiorly by the anterior margin of the inferior 
articular surface. Over this the tendon of the tibialis anticus, and the combined 
fleshy and tendinous parts of the extensor proprius hallucis and extensor com- 
munis digitorum muscles pass obliquely downwards. The posterior surface (facies 
posterior) of the shaft lies between the interosseous ridge externally and the in- 
ternal border on the inner side. Its contours are lable to considerable variation 
according to the degree of lateral compression of the bone. It is usually full and 
rounded above, and flat below. Superiorly it is crossed by the oblique or popliteal 
line (linea poplitea), which runs downwards and inwards, from the fibular facet 
above, to the internal border on a level with the junction of the middle with the 
upper third of the shaft. To this line, as well as to the internal border for some 
distance below it, the soleus muscle is attached. Into the bulk of the triangular 
area above it the popliteus muscle is inserted. Arising from the middle of the 
popliteal line there is a vertical ridge, which passes downwards and divides the 
posterior aspect of the shaft into two surfaces—an external for the tibial origin of 
the tibialis posticus muscle, and an internal for the flexor longus digitorum muscle. 
The inferior third of this surface of the shaft is free from muscular attachments, 
but is overlain by the tendons of the above muscles, together with that of the flexor 
longus hallucis. A large nutrient canal, having a downward direction, opens on the 
posterior surface of the shaft a little below the popliteal line and just external to 
the vertical ridge which springs from it. 
The inferior extremity of the tibia displays an expanded quadrangular form. 
It is furnished with a saddle-shaped articular surface on its under surface (facies 
articularis inferior), which is concave from before backwards and slightly convex 
from side to side. This rests upon the superior articular surface of the body of the 
astragalus, and is bounded in front and behind by well-defined borders. The 
anterior border is the rounder and thicker, and is oftentimes channelled by a groove 
