Zi | THE KNEE-JOINT. 289 
by faintly-marked, almost transverse grooves, which pass across the articular 
surface immediately in front of the intercondylar notch. As a rule marginal 
indentations of the articular surface render the positions of these transverse 
grooves more distinct. 
The patellar portion (Fig. 223) is situated anteriorly, and is common to both 
condyles, although developed to a larger extent in association with the outer condyle, 
on which it ascends to a higher level than on the inner condyle. This surface is 
trochlear, and forms a vertical groove bordered by prominent lateral borders. 
The tibial portion of the articular surface of the femur is divided into two 
articular areas, in relation to the inferior aspects of the two condyles, by the wide 
non-articular intercondyloid notch. These two surfaces are for the most part 
parallel, but in front the internal tibial surface turns obliquely outwards as it 
passes into continuity with the patellar trochlea, while posteriorly, under certain 
circumstances, e.g. the squatting posture, the articular surface of the inner condyle 
may extend to the adjoining portion of the popliteal area of the bone. 
When the joint is in the position of extreme flexion, the patella is brought into 
direct contact with that part of the articular surface on the inner condyle which 
bounds the intercondyloid notch upon its inner and anterior aspects. This relation- 
ship is indicated by the presence of a distinct semilunar facet on the cartilage in 
that situation (Fig. 223). The articular surface of the femur may therefore be 
regarded as presenting femoro-patellar and femoro-tibial areas. 
The patella presents on its posterior aspect a transversely-elongated oval 
articular facet and an inferior rough, triangular, non-articular area. The articular 
facet is divided into two principal lateral portions by a prominent rounded vertical 
ridge. Of these the outer is the wider. A less pronounced and nearly vertical 
ridge marks off an additional facet called the internal perpendicular facet, close to 
the inner margin of the articular surface. Two faint transverse ridges cut off 
narrow upper and lower facets from the general articular surface without encroach- 
‘ing on the narrow innermost vertical facet (Goodsir) (Fig. 223). 
The head of the tibia presents on its superior aspect two condylar articular 
surfaces, separated from each other by a non-articular antero-posterior area, which 
is wider in front and behind than in the middle, where it is elevated to form a 
bifid tibial spine. 
The external condylar facet is slightly concavo-convex from before backwards, 
and slightly concave transversely. This surface is almost circular, and extends 
to the free external border of the tibial head, where it is somewhat flattened. 
Posteriorly the articular surface is prolonged downwards on the tuberosity in 
relation to the position occupied by the tendon of the popliteus muscle. The 
internal condylar facet is oval in outline, and distinctly concave both in its antero- 
posterior and transverse diameters. 
Ligaments.—Like all diarthroses, this joint is invested by an envelope or 
capsule (capsula articularis), which does not, however, entirely surround the joint- 
cavity, for it is absent as a fibrous membrane above the joint-cavity, subjacent to 
the tendon of the quadriceps extensor muscle. Its specially-named bands are not 
of themselves sufficient to form a complete investment, and a capsular membrane, 
which largely consists of augmentations from the fascia lata and the tendons of 
surrounding muscles, supplies the defective areas. Thus, anteriorly, on each side 
of the patella and the ligamentum patelle, expansions of the vasti tendons and 
fascia lata, constituting lateral patellar ligaments, are evident. On the outer side of 
the joint the external lateral ligament is hidden within a covering derived from 
the ilio-tibial band of the fascia lata. On the inner side expansions from the 
tendons of the sartorius and semi-membranosus muscles augment the capsule, which 
here becomes continuous with the internal lateral ligament. Posteriorly the capsule 
also receives augmentation from the tendon of the semi-membranosus muscle, but 
it is very thin subjacent to the origins of the gastrocnemius muscle, where it covers 
the hinder parts of the condyles. Not unfrequently the capsule presents an 
opening of communication between the interior of the joint-cavity and a bursa 
which lies under cover of the inner head of the gastrocnemius muscle. 
The anterior ligament (lic. patelle, Fig. 223), also called the ligamentum 
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