upper mandible in veri/ young Chickens. 435 



vided the proper degree of heat has been uniformly applied, the 

 first perforation in the egg-shell is sometimes seen, and this is 

 made by the chick itself. 



To shew the manner in which this fracture of the shell is 

 effected, I must refer to plate 40, figure 1, of the Philosophical 

 Transactions for the year 1822, as affording an illustration of the 

 particular position of the chicken in the egg. To describe this 

 position it may be stated, that the legs are drawn upwards, the 

 neck bent forwards and downwards, the occipital portion of the 

 head being turned to the left, and pressed at the same time 

 downwards and inwards, the beak will thus be turned upwards 

 and outwards. Upon the curved part of the upper mandible of 

 the chicken, just above the point, there will be seen a small 

 horny scale, nearly circular, having at its centre a hard and sharp 

 projecting point, and by the particular position of the head thus 

 referred to and described it will be found, that this sharp point 

 is brought into constant contact with the inner surface of the 

 shell. 



On the eighteenth day the voice of the chick may be heard, 

 and motions producing certain changes of position are also evident 

 from additional perforations in the shell. 



The form of the young bird being of greater length than width, 

 little alteration takes place in its longitudinal situation, but partly 

 by the act of the hen in occasionally changing the position of the 

 egg as to its upper surface, (which was also obliged to be attended 

 to with those eggs placed in the hatching apparatus) and partly 

 by the efforts of the young bird, its lateral situation is so changed, 

 that this sharp prominence becomes opposed to the shell at various 

 points in a line extending throughout its whole circumference, 

 about one third below the larger end of the egg; and a series of 

 perforations more or less numerous are thus effected by the in- 

 creasing strength of the chick, weakening the shell in a direction 

 opposed to the muscular power of the bird : it is thus ulti* 

 mately enabled by its own efforts to break the walls of its prison ; 

 and these attempts become more effectual from the then brittle 

 state of the shell, owing to the evaporation and absorption of the 



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