a detailed comparative survey of the structure of developing normal and mutant hearts , including the endocardium , its cellular derivatives , and the extracellular matrix , known as cardiac jelly , showed that in the mutant there are fewer than the normal number of endocardial cells lining the heart lumen , the number of mesenchyme cells is reduced , and the cardiac jelly area is greatly enlarged in the posterior part of the truncus adjacent to the ventricle .
C0018787
heart
C0018827
ventricle