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ZOOLOGY. 



head well backwards, the equilibrium may be thus maintained 

 without abandoning the horizontal position (Fig. 293) ; but 

 when the neck is short, the head large, and the toes of mode- 

 rate length, the bird is forced to maintain an almost vertical 

 position (Fig. 294). To maintain their equilibrium, birds 

 place the head under the wing whilst they sleep perched on 

 one foot (Fig. 306). The mechanism by which they stand 

 with such ease and for such a length of time on one foot, is 

 this : the lower extremity of the femur presents a hollow, in 

 which is lodged, during the extension of the limb, the top of 

 the tibia, which cannot quit this cavity but by a muscular 

 effort. The foot once spread out, remains so, requiring no 

 further muscular effort, and consequently giving rise to no 

 fatigue. 



Fig. 293. The Ibis. 



Fig. 293a. Egyptian Ibis. 



[Sacred Ibis of the Egyptians, as we find it represented on the 

 walls of a temple in Upper Egypt, thus proving, according to M. 

 Cuvier, that the Ibis we now find by the banks of the Nile is 

 precisely the same as existed at least 4000 years ago. Together 

 with this outline by the Coptic artist, M. Cuvier, in his great 

 work (Ossemens Fossiles) gives a drawing of the Numenian Ibis of 

 modern zoologists which he considers as the identical sacred Ibis 

 of the Egyptians. The Ibis represented in Fig. 293 I take to 

 be a drawing of the Numenian Ibis. I met with various species 

 of the Ibis in Southern Africa by the banks of the Great Fish 

 River, Bosjieman River, &c. They frequented the kraals of 



