THE TIBIA. 227 
for the attachment of the anterior ligament of the joint; further, it is occasionally 
provided with a pressure facet caused by the locking of the bone against the neck 
of the astragalus in extreme flexion. Externally the edge of the articular area 
corresponds to the base of the triangle formed by the splitting of the interosseous 
ridge into two parts. Where these two lines join it, both in front and behind, the 
bone is elevated into the form of tubercles, in the hollow between which (incisura 
fibularis) the lower end of the fibula is lodged, being held in position by powerful 
ligaments. The cartilage-covered surface occasionally extends for some little 
distance above the base of the triangle. Internally there is a down-projecting 
process, called the internal malleolus (inalleolus medialis), the inner aspect of which 
is subcutaneous and forms the projection of the inner ankle. Its external surface 
is furnished with a pyriform facet (facies articularis malleolaris), confluent above 
with the cartilage-covered area on the inferior extremity of the shaft; this 
articulates with a corresponding area on the inner surface of the body of the 
astragalus. Inferiorly the malleolus is pointed in front, but notched behind for 
the attachment of the internal lateral hgament of the ankle. Running obliquely 
along the posterior surface of the malleolus there is a broad groove (sulcus 
malleolaris) in which the tendons of the tibialis posticus and flexor longus 
digitorum muscles are lodged; whilst a little to the fibular side of this, and 
running downwards over the posterior surface of the lower extremity of the bone, 
there is another groove, often faintly marked, for the lodgment of the tendon of 
the flexor longus hallucis muscle. The proportionate length of the tibia to the 
body height is as 1 is to 4°32-4°80. 
Arterial Foramina.— Nutrient canals are seen piercing the upper extremity of the bone 
around its circumference and above the tubercle. The floors of the intercondylic fossee are also 
similarly pierced, and there is usually a canal of large size opening on the summit of the spine. 
Two or three foramina of fair size are seen running upwards into the substance of the bone a little 
below and to the inner side of the tubercle, while the principal vessel for the shaft passes down- 
wards into the bone on its posterior surface, about the level of the junction of the upper and 
middle thirds. The inner surface of the internal malleolus, as well as the anterior and posterior 
_ borders of the inferior extremity, are likewise pitted by the orifices of small vascular channels. 
Connexions.—Superiorly the tibia supports the condyles of the femur, and is connected in 
front with the patella by means of the patellar ligament. Articulating externally with the 
fibula above and below, it is united to that bone throughout nearly its entire length by the inter- 
osseous membrane. . The crest and internal surface can be readily examined, as they are sub- 
cutaneous, except above where the internal surface is overlain by the thin tendinous aponeurosis 
of the muscles passing over the inner side of the knee. The form of the lower part of the knee in 
front is determined by the tuberosities on either side crossed mesially by the ligamentum patellie. 
Inferiorly the internal malleolus forms the projection of the inner ankle, which is wider, not so 
low, less pointed, and placed in advance of the projection of the outer ankle. The front and 
back of the lower end of the bone are crossed by tendons, which mask to a certain extent its 
form. 
Architecture.—The shaft of the bone is remarkable for the thickness and density of the 
osseous tissue which underlies the crest. The posterior wall is stout, but the internal and 
external walls are thinner. The several walls are thickest opposite the middle of the shaft, and 
thin out above and below where the shaft unites with the epiphyses. The medullary canal, 
narrow and circular in the middle of the bone, increases in all its diameters above and below, 
and reaches to within 25 to 3 inches of either extremity. Superiorly the arrangement of 
the lamellz of the spongy tissue resembles a series of arches springing from the dense outer walls. 
These form a platform on which the superior epiphysis rests, the spongy tissue of which displays 
a more or less vertical striation. This is much more compact under the condylic surfaces, the 
superticial aspect of which is formed by a thin layer of dense bone. The spine and tubercle are 
also formed of compact tissue, whilst the circumference of the tuberosities is covered by a 
thinner and less dense wall. In the lower end of the shaft the spongy tissue, of a loose and 
cellular character, is arranged in vertical fibres, blending inferiorly with the closer tissue of the 
inferior epiphysis, the articular surface of which is covered by a thin but dense layer. 
In the adult bone the nutrient canal for the shaft is embedded in the dense posterior wall for 
the space of two inches. 
Variations.—The tibia is often unduly laterally compressed, leading to an increase in its 
antero-posterior diameter as compared with its transverse width. This condition is more 
commonly met with im the bones of prehistoric and savage races than in modern Europeans. 
Attention was first directed to this particular form by Busk, who named the condition 
‘platycnemia. The general appearance of such tibize resembles that seen in the apes, and 
depends on an exceptional development of the tibialis posticus muscle, though, as Manouvrier 
has pointed out, in apes this is associated with the direct action of the muscle on the foot, as in 
climbing, whereas in man, as a consequence of the bipedal mode of progression, the muscle is 
employed in an inverse sense, viz. by steadying the tibia on the foot, and thus providing a fixed 
