150 



HABITS OF BIRDS. 



becomes the left ventricle ; the third part (bulbus 

 aortce) is considerably bulged out. It is remarka- 

 ble that the heart at this period projects beyond 

 the breast, and beats in triplets : first, on re- 

 ceiving into the auricle the blood from the veins; 

 secondly, on discharging this blood into the arte- 

 ries ; arid thirdly, on forcing it into the vessels 

 of the navel, motions which will continue for 

 twenty-four hours, if the embryo be taken out of 

 the egg. The veins and arteries may now also be 

 seen branching over the surface of the brain, and the 

 spinal marrow beginning to extend along the back ; 

 or rather, as has been beautifully shown by Marcel 

 de Serres*, Tiedemannt and CarusJ, the spinal 



An Egg opened thirty-six hours after incubation, with a magnified view of 

 the Embryo Chick, in which is shewn the first appearance of the principal 

 blood-vessels. 



* Du Cerveau, Paris, 1826 ; an^Sur leCervelet, Paris, 1823, 

 f Geschichte des Gehirns des Foetus, 4to. Leipzig. 

 J Comparative Anatomy, by Gore. 



