312 



EMBETOLOQT. 



the advancing laminae of the medulla oblongata as the crura 

 cerebri ; it is open superiorly, and extends, as the third ventri- 

 cle, with a wide opening into the infundibulum, which on the 

 second day was directed straight downwards, but which now, 

 from the great bending in of the head, is turned backwards, 

 and even upwards. In this cell, which was the first formed, 

 and foremost cere'bral cell (fig. 334, c? 1 ), the thalami make 

 their appearance towards the end of the period. The most 



Fig. 342 A. Embryo of the fowl of the fifth day, much magnified ; 

 after Huschke (Isis, 1828, 163.) a, a, hemispheres; b, corpora quad- 

 rigemina; e, upper jaw; d, under jaw; e, first branchial arch (os 

 hyoides) ; f, meatus auditorius externus ; 1 , </ 2 , g 3 , first, second, and 

 third branchial fissures ; A 1 , A 2 , A 3 , the three branchial arteries ; i, the 

 heart ; k, the eye, with the cleft 1; m, descending aorta ; D, cavity of the 

 mouth and fauces ; n, acoustic pouch. 



Fig. 342. B (after Huschke), front view of the embryo of the fowl, of 

 the fourth day; a, hemispheres; b, corpora quadrigemina ; c, eye ; d, 

 upper jaw; e, lower jaw; /, enlargement of the os hyoides; g, ventricle 

 of the heart ; A, atrium cordis ; D, oral aperture and faucial cavity. 



