310 THE REASON WHY 



"The eye is not that which sees; it is only the organ by 

 which we see. The car is not that which hears, but the organ 

 by which we hear ; and so on of the rest." REID. 



velocity, they require for their safety, as well as for assisting them 

 in descrying their food, a power of seeing at a great distance. 



938. Two peculiarities are found in the eyes of birds. The one is a bony, yet, in 

 most species, a flexible rim or hoop, surrounding the broadest part of the eye, 

 which, confining the action of the muscles to that part, increases the effect of their 

 lateral pressure upon the orb. by which pressure its axis is elongated for the 

 purpose of looking at very near objects. The other peculiarity is an additional 

 muscle to dra**, on occasions, the cystalline lens back, and to fit the same eye for 

 the viewing of very distant objects. By these means, the eyes of birds can paes 

 from one extreme to the other, on a scale of adjustment as convenient as it 

 is remarkable. 



989. Why is the hearing of birds dependent upon the internal 

 structure, rather than the outward development of the organ ? 



Because, if the external ear existed as in quadrupeds, it ivould 

 obstruct the rapid progress of birds through the air, and be 

 inconvenient in other respects. This appendage is therefore with- 

 held, but is amply compensated for by a peculiarity in the internal 

 structure, which enables them to hear with perfect distinctness 



. 990. Why do birds perch with their faces to the wind ? 



Because, if a bird were to roost with its tail to the wind it 

 would frequently be driven from its perch : the wind would, by 

 turning the feathers, and even getting under the wings, have 

 great power ; and the action of that power would unbend the 

 legs, and thereby loosen the feet from the perch. But, by perching 

 with its head to the wind, the latter becomes a means of 

 stability to the bird. 



991. The bir% keeps its hold on the perch by tendinous elasticity ; the flexure of 

 the neck is beyond that position which would be repose in a quadruped, so that the 

 tendons of the extensors are tightened ; and any cause which agitates the perching 

 feet, at the same instant brings the neck into action, and extends, elevates, or 

 depresses the head, to the exact extent which the balance requires. Thus, there is, 

 in the very structure of the bird, a means of resisting any casualty that might drive 

 it from its perch, and that without the exercise of any more volition tliin 

 accompanies the breathing of a human being when asleep. 



