4 
OSTEOLOGY. 
internal to the ridge which springs inferiorly from the malleolar subcutaneous 
STYLOID PROCESS 
\ 
FACET FOR TIBIA_ 
Heap 
Soleus 
Extensor longus ____ 
digitorum | i 
INTEROSSEOUS RIDGE 
Extensor proprius — 
hallucis 
Tibialis posticus 
NUTRIENT 
FORAMEN 
INTEROSSEOUS 
RIDGE 
Flexor longus 
hallucis 
Peroneus tertius” 
RovuGH SURFACE 
FOR INTER 
OSSEOUS 
LIGAMENT 
FACET FOR 
ASTRAG ALus—!@ 
7] 
NN 
ST. 
Fossa 
FOR 
ATTACH. 
OF PO 
PART OF 
EXTERNAL 
MALLEOLUS 
Fic. 171.—RIGHT FIBULA AS 
SEEN FROM THE INNER SIDE. 
is oftentimes called the internal border (crista medialis) ; 
mapped off, the internal surface. 
triangular surface, notwithstanding the differences in 
width of the surface which separates the lines, or their 
occasional coalescence above. 
The position of the interosseous ridge enables us at 
once to separate the flexor aspect of the bone from its 
extensor surface, using these terms in relation to the 
movements of the ankle. 
The use of these terms is not, strictly speaking, correct, and they 
are here used in a phy siological and not ina morphological sense. 
The anterior surface of the leg is the true extensor surface and 
is comparable with the posterior surface of the forearm, the change 
in position having been brought about developmentally by pie - 
ence in the rotation of the limbs. Flexion of the ankle, so called, 
is in reality an extensor movement, and corresponds to extension at 
the wrist; see Humphry, Journ. Anat. and Physiol., vol. xxviii. p. 15. 
In addition, there is the peroneal surface, which cor- 
responds to the outer side of the shaft. Starting then at 
the interosseous ridge, and passing forwards round the 
outer side of the shaft, the flexor surface is the first met 
with; this is bounded externally by the anterior border, 
and, as has been said, may be either of considerable width 
or almost linear. From this arises the extensor com- 
munis digitorum, together with the peroneus tertius and 
the extensor proprius hallucis muscles, which, though 
extensors of the toes, are also flewors of the ankle. 
The anterior border serves for the attachment of the 
intermuscular septum, which separates the foregoing 
vroup of muscles from that which hes along the outer side 
of the shaft, viz. the peroneus longus and brevis muscles. 
The surface from which these arise is limited behind by 
the posterior border, which is usually sharp and well 
defined below, where it is continuous with the bone im- 
mediately above the pit on the inner surface of the lower 
extremity, whilst it tends to be less distinct and more 
rounded above where it runs into the base of the styloid 
process. In its upper third or fourth this border is often 
rough and tubercular where it serves for the origin of 
the soleus. The outer or peroneal surface is somewhat 
twisted, being directed rather forwards above, but tend- 
ing to turn backwards below where it becomes continuous 
with the groove which courses along the back of the 
external malleolus and which lodges the tendons of the 
peroneus longus and brevis muscles. The remainder of 
the shaft, included between the posterior border behind 
and the interosseous ridge in front and internally, is the 
extensor surface, for here arise the several muscles whose. 
action in part is to extend the ankle. This surface is 
cut up by a curved ridge often the most prominent and 
outstanding on the bone, and hence frequently mistaken 
by the student for the interosseous ridge; it serves to 
define the area for the origin of the tibialis posticus, and 
arises below from the poster ior border of the interosseous 
ridge at the junction of the middle and inferior thirds. 
of the shaft, curves a little backwards, and passing 
upwards and obliquely forwards again joins the inter- 
osseous ridge once more in the region of the neck. This 
and the surface so 
The ridge itself serves for the attachment 
