THE MUSCLES OF THE LEG AND FOOT 333 



Blood-supply. — Femoral and anterior femoral arteries. 



Nerve-supply. — Femoral nerve. 



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

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



Origin. — (1) The anterior surface of the femur, from the proximal to the distal 

 fourth; (2) the tendinous covering of the vastus medialis. 



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 

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

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



Relations. — Medially, the vastus medialis; laterally, the vastus lateralis; 

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



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



Nerve-supply. — Femoral nerve. 



The patellar ligaments are to be regarded as tendons of the quadriceps which communicate 

 the action of the latter to the tibia, the patella being intercalated as a sesamoid bone. 



3. Capsularis (Fig. 291).- — This is a small fusiform muscle (scarcely as large 

 as one's finger), which arises by a thin tendon on the ilium immediately above the 

 outer tendon of the rectus femoris. Its delicate tendon of insertion dips in between 

 the vastus intermedius and lateralis and is attached to the proximal third of the 

 anterior surface of the femur. It passes over the outer side of the hip joint, to the 

 capsule of which some fibers are attached. Sometimes the muscle has two dis- 

 tinct 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. It is related laterally to the gluteus profundus and vastus lateralis, 

 medially to the rectus femoris and vastus intermedius and the hip joint. 



V. THE MUSCLES OF THE LEG AND FOOT 



The muscles of this region cover almost all of the tibia except its medial face, 

 which is largely subcutaneous. As in the forearm, the muscles fall into two groups, 

 a dorso-lateral and a plantar. The muscles of the first group are extensors of the 

 digit and flexors of the hock, those of the second have the opposite action. 



A. DoRSO-LATERAL GrOUP 



1. Long digital extensor (M. extensor digitalis longus).^ — This muscle is sit- 

 uated superficially on the dorso-lateral aspect of the leg, and is provided with a long 

 tendon which passes down over the front of the tarsus, metatarsus, and digit. 



Origin.- — The extensor fossa of the femur. 



Insertion. — (1) The extensor process of the third phalanx; (2) the dorsal sur- 

 face of the proximal extremities of the first and second phalanges. 



Action. — To extend the digit and flex the hock. It also assists in fixing the 

 stifle joint. 



1 While it is true that the separation of the intermedius is never entirely a natural one in the 

 horse, 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. 



2 Also known as the rectus parvus. 



' Also termed the extensor pedis or the anterior extensor of the phalanges. 



