of the Leg of the Ostrich, 263 



in the summer of 1863. Mr. Macalister availed himself of the 

 opportunity, and has laid before the Royal Irish Academy such 

 results of his dissections as seemed to him most worthy of 

 record. 



My own attention was directed especially to the investigation 

 of the muscular mechanism of the leg of the Ostrich, which I 

 have long regarded as one of *the most interesting pieces of 

 mechanism in the animal kingdom. I was fortunate enough to 

 discover, in the digastric rectus femoris muscle, what I believe 

 to be the key to the explanation of the complicated muscular 

 apparatus of the Ostrich's leg. 



The leg of the Ostrich is to be regarded as a long rod bent at 

 four distinct points, which attains its greatest amount of shorten- 

 ing or bending at the moment the foot touches the ground, and 

 which is suddenly straightened or elongated by the simultaneous 

 contraction of all the muscles. The effect of the sudden elonga- 

 tion of the leg is to throw the whole body of the bird forward, 

 as if from a catapult, from the point of support of the foot ; and 

 while the body of the animal is thus projected through the air, 

 the antagonist muscles that flex the several joints come into 

 play, and are assisted in their action by some very remarkable 

 contrivances in the heel-joint, which I shall describe and figure. 



It is necessary to the perfection of the mechanism that the 

 greatest possible amount of muscular force shall be expended in 

 straightening or unbending the legs, alternately projecting the 

 animal from foot to foot along the ground, the leg being at its 

 maximum of flexure at the moment of touching the ground, and 

 at its maximum of elongation at the moment of leaving it ; and 

 also that the minimum possible amount of force shall be ex- 

 pended in flexing each leg preparatory to its next spring, which 

 must take place on its next touching the ground. 



I shall show that the leg of the Ostrich fulfils these two con- 

 ditions of perfect mechanism ; but, before doing so, I shall de- 

 scribe in detail the muscles employed by the Ostrich in the act 

 of running. 



Part I. Description of the Muscles, 



1. A muscle, which must be regarded as a combined tensor 

 vaginse femoris, glutseus maxim us, and agitator caudse, takes its 

 origin from the whole length of the posterior edge of the ilium 

 (and first two caudal vertebrse) forwards to the commencement 

 of the symphysis iliaca (PI. VI. fig. I.), and is inserted as fol- 

 lows : — [a) The tensor vaginse portion is inserted into a broad 

 tendon, passing over the outer side of the knee, this tendon 

 forming also one of the origins of the gastrocnemius, {b) The 

 gluteal portion of the muscle is inserted partly like («), and 



