FUSION OF CARDIAC ANLAGES IN THE CAT 



()7 



degree its vontml Mirfaco. 'Vhv drawing is greatly foreshort- 

 ened. The bulbar segments are approximated but their lumina 

 are still completely separated by an endothelial partition. The 

 right bulb has a slightly greater cross-section than the left (fig. 

 14) and in its terminal segment the left is slightly irregular in 

 contour as can be seen in the illustration of the model. These 

 changes, though small, foreshadow the reduction of the left bulb 



Fig. 13 Reconstruction of the lumen of the heart in a cat embrj-oof fourteen 

 pairs^of somites. Columbia Collection, No. 188. X 300. Reduced one-half. 

 1, Right bulb; 2, left bulb; 3, left ventricle; 4, right ventricle; 5, fusion between 

 isthmi; 6, fusion between ventricle; 7, fusion at cardio-venous angles; 8, left 

 omphalo-mesenteric vein; 9, light omphalo-mescnteric vein. 



in later stages. The isthmus of the left side is strongly kinked 

 by the deepening left bulbo-ventricular sulcus, while the open- 

 ing out of the sulcus of the right side places that bulb under more 

 favorable conditions as regards flow. The area of fusion be- 

 tween the isthmi has greatly increased. 



The ^'entricles are pyramidal in form, tapering toward the 

 isthmus and caudad and prolonged in strong angular projec- 



