Page 362. 
102 NOTES ON AN OSTRICH LATELY LIVING 
tended; there is a smaller “‘sesamoid”’ cartilage for the external 
digit. A small muscle arises from the larger cartilage and by a few 
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 in- 
serted 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 provided 
with a second muscular belly (p. 53), which does not all describe its 
condition in my specimen. Heconsiders this “ digastric rectus femoris 
muscle” to be “‘the key to the explanation of the complicated museu- 
lar 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 patelle, braces up the heel-joint, and gives the signal 
for the m. gastrocnemio-soleus and other associated muscles to con- 
tract, and thus produces what may be regarded as one of the most 
striking phenomena in nature, viz., that the delicate bones and liga- 
ments 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 Professor 
Owen says is used in perching, by flexing the toes when the knee is 
bent (loc. 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. 
* The Rey. S. Haughton, M.D., “‘ Notes on Animal Mechanics.—No. 3. On the 
Muscular Mechanism of the Leg of the Ostrich,” “‘ Proceedings of the Royal Academy 
of Dublin,” IX. Part 1 (1865). 
