298 



HEART FIELD OPERATION 



THE PRODUCTION OF DOUBLE HEARTS 



This operation may be performed on the Anura (stage #16) or on the Urodela (stages #22- 

 #25) although the latter are preferred because the development of the heart can be fol- 

 lowed through the transparent skin of the ventral side without exploratory incisions. 



Place the embryo in a Permoplast depression in such a position that the ventral heart 

 forming areas faces upward. Locate the exact position of the future heart and with sharp 

 glass needles make an incision posterior to the region of the thyroid anlage and deep 

 enough to reach the grayish endoderm of the pharyngeal floor. Carry this incision pos- 

 teriorly to the position of the liver anlage. With a fine hair loop clean out the loose cells 

 in the mid-ventral line, forming a channel. Leave the lateral mesenchyme intact. 



NORMAL DEVELOPMENT OF HEART 



PHARYNGEAL ENOOCERM 

 . ENDOCARWUM 



MVOCAROUM 



PERICARDIAL CAVITY 



POINT OF INSERTION OF 

 BLOCK OF INERT TISSUE 



TUBULAR HEART 



CONUS ARTERIOSUS 



VENTRICLE 

 SJNUS VENOSUS 

 VITELLINE VEIN 



FRONTAL VIEW OF EARUf HEART 



BLOCKING TISSUE 



MNG TISSUE 



PARTIAL DUFUCATION OF HEART 



COMPLETE OUPUCATION OF fCART 



REORJVN FROM EXMAN '25 



EXPERIMENTAL DUPUCATION OF hCART 



From a second embryo of the same species but of a later stage of development, remove 

 a strip of notochord long enough to fill the excavated channel. Insert it into the operated 

 embryo between the lateral heart rudiments, replace the ventral ectoderm, and hold the 

 flap of ectoderm in position for 20 to 30 minutes by i;neans of a Brucke or lens paper 

 bridge. Alternative procedures may include flank ectoderm with underlying somite meso- 

 derm instead of notochord. Return the embryo to the normal culture medium after the 

 wound has healed over. 



Should the above procedure fail to produce a double-hearted embryo, proceed with a more 

 extensive operation on an embryo one stage younger. Remove the ecto-mesoderm by 

 making a longitudinal slit from a position between the suckers posteriorly about 1/3 of the 

 length of the embryo. Carry the cut dorsally on one side of the embryo to the ventral 

 limits of the closed medullary fold, then forward, to complete a trapezoid. Avoid as 

 much of the head ectoderm as possible. After outlining this area, carry the incision 

 deeper until all mesoderm on the side of the operation is circumscribed. Remove this 



