286 FASCIA AND MUSCLES OF THE HORSE 



Relations. — Externally, the fascia lata and skin, tensor fasciae latse, superficial 

 gluteus, and biceps femoris; internallj', the femur and femoro-patellar joint capsule, 

 the rectus femoris, vastus intermedius, and the iliaco-femoral artery. 



Blood-supply. — Iliaco-femoral artery. 



N^erre-supply. — Femoral nerve. 



(3) Vastus intemus (s. medialis). — This is smaller than the preceding muscle, 

 and lies in a similar position on the inner side of the thigh. 



Origin. — The internal surface of the femur, from the neck to the distal third. 



Insertion. — (1) The upper part of the inner border of the patella and its carti- 

 lage; (2) the tendon of the rectus femoris. 



Action. — To extend the stifle joint. 



Structure. — This is very similar to that of the vastus externus. It is, how- 

 ever, more difficult to separate from the intermedius, because many fibers of the 

 latter arise on the tendinous sheet which covers the contact surface of the inner 

 vastus. Its insertion into the patella is chiefly by means of a broad strong tendon. 

 From the deep face fleshy fibers are inserted also into the femoro-patellar capsule. 



Relations. — Internally, the skin and fascia lata, the iliacus, sartorius, pectineus, 

 and adductor, the femoral vessels and saphenous nerve; externally, the femur, 

 femoro-patellar joint capsule, rectus femoris, and vastus intermedius, the anterior 

 femoral artery, and branches of the femoral nerve. 



Blood-supply. — Femoral and anterior femoral arteries. 



Nerve-supply. — Femoral nerve. 



(4) Vastus intermedius (Crureus). — This muscle is deeply situated on the 

 anterior face of the femur, and is entirely covered by the preceding heads. 



Origin. — (1) The anterior and external surfaces of the femur, from the proximal 

 to the distal fourth ; (2) the aponeurosis of the vastus internus. 



Insertion. — (1) The base of the patella; (2) the femoro-patellar joint capsule. 



Action. — (1) To extend the .stifle joint; (2) to tense (raise) the femoro-patellar 

 capsule during extension of the joint. 



Structure. — The muscle is usually quite difficult to isolate from the other vasti, 

 so that many since Giinther have declared it an artefact.^ It is entirely fleshy, and 

 is small at its proximal end, but when traced downward increases in bulk by the 

 accession of fibers arising on the femur and the tendinous covering of the vastus 

 internus. The terminal part is intimately adherent to the femoro-patellar joint 

 capsule, where the latter bulges upward above the level of the patella. 



Relations. — Internally, the vastus internus; externally, the vastus externus; 

 anteriorly, the rectus; posteriorly, the femur and femoro-patellar capsule. 



Blood-supply. — Iliaco-femoral and anterior femoral arteries. 



Nerve-supply. — Femoral nerve. 



The straiglit ligamonts of tlic patolla are to he regarded as tendons of the quadriceps which 

 communicate the action of the latter to tlie tibia, the patella being intercalated as a sesamoid 

 bone. 



3. Capsularis (Fig. 154) (Rectus parvus). — This is a small muscle (scarcely as 

 large as one's linger), which arises on the ilium immediately above the outer tendon 

 of the rectus femoris, and passes down between the vastus internus and externus to 

 bo inserted into the anterior surface of the femur. It passes over the front of the 

 hij) joint, to the cajisule of which some fibers are attached. Sometimes the muscle 

 has two distinct heads, in which case the additional head arises between the two 

 tendons of origin of the rectus femoris. Its action may be to raise the capsule 

 during flexion of the joint. 



J While it is true that the separation of the intermedius is probably never entirely a natural 

 one in the hor.se, it varies in individual cases, and is usually clear on cross-sections. In some 

 subjects it is possible to separate another slip which may represent the articularis genu of man. 



