734 THE ANATOMY OF THE RUFFED GROUSE 



Id tlu' tendon of M. flexor profundus and is connected to that tendon by the vinculum. The 

 tendon perforates the tendon of M. flexor brevis digiti I to insert on the ungual phalanx. 



M. extensor brevis digiti I originates from the head of the tarso-nielalarsus on the dorsal 

 side and the adjoining part of the bone. This is a small muscle whose tendon passes 

 niesiall) to the accessory metatarsus to insert on the basal phalanx. 



M. extensor brevis digiti III is small and lies on the distal one-fourth of the anterior sur- 

 face of the tarso-metatarsus. The tendon inserts on the basal phalanx. The origin is more 

 extensive in Gallus and the muscle is larger. There is only one short extensor of digit III. 

 Hudson^' points out that this is true of all Neognathae examined. The term "brevis" seems 

 preferable to "proprius". 



M. extensor brevis digiti IV originates at the proximal end of the anterior surface of the 

 tarso-metatarsus. The tendon soon forms and passes through a foramen of the metatarsus to 

 insert on the ventro-medial surface of the basal phalanx. 



M. flexor brevis digiti I originates at the proximal end of the posterior surface of the tarso- 

 metatarsus. The muscle is on the ventral internal side. There are two distinct, though small, 

 heads whose tendons soon fuse. The muscle is bounded internally by the ridge of bone on 

 the ventral surface of the tarso-metatarsus. Its tendon passes on the ventral surface to insert 

 on the basal phalanx. The tendon is perforated at its insertion for the passage of tlie tendon 

 of M. flexor longus digiti I. In Gallus, there is no ridge of bone. 



M. flexor brevis digiti II was not found. 



M. adductor digiti II is absent as in PedioeceteS^. 



M. adductor digiti IV was not found. 



M. adductor digiti II is a very small muscle on the internal distal one-fourth of the anterior 

 surface of the tarso-metatarsus. Its slender tendon inserts on the basal phalanx. It is well 

 developed in Gallus. 



M. abductor digiti IV matches the position of M. flexor brevis digiti I, lying on the external 

 edge of the ventral surface. The tendon passes to the lateral side of the proximal end of 

 the basal phalanx, where it is inserted. 



Movement of Leg. The manner in which movement of the leg is accomplished may be 

 briefly described as follows. The ruffed grouse possesses all the leg muscles which are pres- 

 ent in birds except for certain ones associated with the digits. This indicates a great free- 

 dom of motion and a lack of specialization for any particular direction of movement. Each 

 joint has great flexibility. It has been pointed out that in the grouse-like birds, the muscles 

 for rotation and toe movement are, in comparison with other birds, powerfully developed. 

 This is correlated with pecking and scratching. 



The rotation of the femur in the ac<"tainilum is performed primarily by Mm. iliacus. 

 gluteus profundus, obturator, and flexor ischio-femoralis. M. piriformis is a weak abductor 

 as is M. psoas which also tends to flex the femur on the pelvis. Forward movement of the 

 femur is produced bv M. extensor iliotibialis anterior and. to some extent, by the anterior 

 part of M. extensor iliotibialis lateralis. The backward movement and flexion of the femur is 

 performed by M. adductor superficial is primarily, but assisted by M. caudofemoralis and 

 M. flexor cruris lateralis. M. vastus medialis rotates the tibia inward. 



The flexion of the tibia on the femur is performed by M. flexor cruris medialis and M. 

 flexor cruris lateralis. The extension of the tibia is caused by M. vastus lateralis. The tarso- 



