COMPARATIVE ANATOMY 39 



19. Adductor Longus. — This is a small muscle anterior to 

 and slightly overlapping the aductor femoris. It originates 

 with the pectineus from the cranial border of the pubis and 

 inserts by a thin aponeurosis on the femur. 



Action: to adduct the thigh. 



20. Pectineus. — ^This is the last and smallest of the muscles 

 on the caudal side of the femur. It is sometimes entirely fused 

 with the adductor longus. It originates from the cranial border 

 of the pubis, and inserts on the femur. 



Action: to adduct the thigh. 



21. Iliopsoas. — This is the equivalent of two human mus- 

 cles, the iliacus and the psoas. It emerges from the body cavity 

 and inserts on the lesser trochanter of the femur. It originates 

 from the centra and transverse processes of ten vertebrae. Do 

 not trace it to its origin; it will be seen again in the study of the 

 internal anatomy. 



Action: to rotate flex the thigh. 



22. Quadriceps Femoris. — This is the large mass of muscle 

 covering the whole cranial surface of the femur. It consists 

 of four parts, each of which may be considered a separate muscle, 

 with a common insertion on the patella. The vastus lateralis 

 forms the lateral face of this muscle. It originates on the lateral 

 side of the great trochanter and shaft of the femur. The vastus 

 medialis forms the medial face of the quadriceps femoris, and 

 has its origin from a long area on the median side of the femur. 

 The rectus femoris lies between the vastus lateralis and vastus 

 medialis, and originates from a triangular area just anterior to 

 the acetabulum. It unites with the vastus lateralis about two- 

 thirds the way down the femur. Cutting the rectus femoris 

 through the middle will expose part of the vastus intermedius, 

 which lies beneath it. The vastus intermedius originates from 

 nearly the whole length of the femur. It is usually difficult to 

 separate it cleanly from the vastus medialis. At the proximal 

 end of the quadriceps femoris, between the vastus lateralis and 

 rectus femoris, the capsularis muscle may be seen. 



Action: to extend the shank. 



23. Obturator Externus. — Cut transversely through the 

 middle of the semitendinosus, semimembranosus, and adductor 



