362 ON AN OSTRICH LATELY IN THE SOCIETY'S COLLECTION. [Mar. 5, 



fibres from the smaller one, and is inserted into the anterior surface 

 of the flexor profundus tendon. The flexor magnus is pierced, as it 

 passes through the sesamoid sheath or pulley, by the tendons of 

 flexor profundus and flexor perforans, and ends by dividing into two 

 slips, which are inserted into the proximal end of the second phalanx 

 of the internal digit. 



Mr. Macalister gives as the origin of the flexor magnus the deep 

 pit above the condyles of the femur, the tendon of the rectus femoris, 

 the external lateral ligaments, and the back of the fibula. In the 

 specimen which I dissected, the tendon of the rectus femoris was 

 much smaller than the tendinous head of the flexor profundus, and 

 was inserted into it, which is an arrangement differing very slightly 

 from its usual insertion in birds, which is, I believe, into the fleshy 

 part of flexor magnus (Owen, Anat. Vert. vol. ii. p. 107). 



The Rev. S. Haughton* describes the rectus as becoming pro- 

 vided with a second muscular belly (p. 53), which does not at all 

 describe its condition in my specimen. He considers this " digastric 

 rectus femoris muscle "to be " the key to the explanation of the 

 complicated muscular apparatus of the Ostrich's leg " (p. 50). 

 Speaking of it, he says, " it acts before the extensor muscles come 

 into full play ; it binds down the two patellae, braces up the heel-joint, 

 and gives the signal for the m. gastrocnemio-solaeus and other asso- 

 ciated muscles to contract, and thus produces what may be regarded 

 as one of the most striking phenomena in nature, viz. that the deli- 

 cate bones and ligaments of a bird's leg, acted on by muscles equal 

 to those influencing a horse's hind leg, shall remain uninjured under 

 the sudden action of forces the slightest error in the application of 

 which would break to pieces the machinery on which they act." 

 This arrangement of the rectus, which Mr. Haughton considers so 

 important, is only a well-developed form of what is found in most 

 birds, and which Prof. Owen says is used in perching, by flexing the 

 toes when the knee is bent (Joe. cit.). 



Mr. Macalister does not mention the muscle from the flexor profun- 

 dus tendon to the sesamoid cartilage ; but says that the flexor magnus 

 sends a slip to it. The function of this muscle must be to keep the 

 pulley-like sesamoid cartilage firmly in its place when the toes are 

 extended preparatory to their flexion in the spring of the bird. 



Flexor digiti interni arises from the outside of the tubercle of the 

 tibia, and from the tendon of the quadriceps extensor ; the tendon 

 passes through the gastrocnemial sheath and the sesamoid pulley. 

 It pierces the flexor magnus, receiving a tendinous slip from it, and 

 then spreads out and binds the tendon of flexor profundus to the 

 grooved under surface of the second phalanx of the internal digit, and 

 is inserted by two slips into the proximal end of the third phalanx. 



Flexor digiti externi arises from the posterior surface of the distal 

 end of the femur, and from the tendinous head of flexor magnus. 

 It passes through the gastrocnemial sheath, pierces the tendon of 



* The Rev. S. Haughton, M.D., "Notes on Animal Mechanics. — No. 3. On 

 the Muscular Mechanism of the leg of the Ostrich," Proc. Eoy. Acad. Pub. 

 vol. is. part 1 (1865). 



