Development of heart in Frog
The heart is the first organ to start functioning because it has to circulate blood which brings nourishment from the endodermal cells to the other parts of the embryo. The initial development of heart is similar in all vertebrates. The first rudiment of heart develops after neurulation in the region beneath the pharynx, from the mesenchyme and mesoderm. The heart of frog develops at the ventral side of pharynx. It is formed by mesenchyme cells. The mesenchyme cells accumulate at the mid-ventral line of pharynx and form a longitudinal strand of tissue called the rudiment of endocardium. Soon the endocardial cells get arranged in the form of a thin walled tube, the lumen of which later develops into the cavity of the heart. While the endocardial tube is being formed, the mesoderm of both sides unite above and under the endocardial tube and a cavity called pericardial coelom is formed around the latter. The visceral layer of mesoderm envelops the endocardial tube and gives rise to its muscular walls or myocardium and also its close fitting covering called the visceral pericardium.