Question

Pylangium in frog occurs in
A. Conus arteriosus
B. Sinus venosus
C. Atrium
D. Ventricle

Answer 1

Hint: Pylangium is a muscular portion of the arterial trunk in immediate reference to the ventricle of the center in some lower vertebrates.

Complete answer:
Heart of frog is three chambered. It is a red colored conical muscular organ situated mid-ventrally within the anterior part of the body cavity in between two lungs. It is enclosed in two membranes-an inner epicardium and outer pericardium.

Structure of heart:
External structure:
> The External heart seems like a triangular structure. It is 3 chambered.
> Its anterior end is broad and the posterior end is somewhat pointed.
> The anterior part is named auricles whereas the posterior part is named ventricles.
> Auricles are two chambered: left and right auricles.
> Ventricle is single chambered. It's the most vital part of the heart. It's conical in shape with thick muscular walls and clearly separated from auricles by coronary sulcus.

Heart of frog consists of two additional chambers:
1. Sinus venosus:
> On the dorsal surface of the heart, two precaval and a postcaval fused to make a wide chamber called sinus venosus.
> It is a thin walled dark colored triangular structure which opens into the right auricle.
> It receives impure blood from all parts of the body and pours it into the right auricle.

2. Truncus arteriosus:
> It is a tubular structure that arises from the right side of the ventricle.
> It extends forward over the proper auricle and at last divides into two branches to make aortic trunks.


Internal structure of truncus arteriosus: The truncus arteriosus is split into two unequal parts:
Conus arteriosus or pylangium-
> It is the part near the ventricle- proximal part.
> It is a long broad and thick walled structure. It contains an outsized cavity called pylangium. It's supplied with semilunar valves at both ends.
> Pylangium is incompletely divided by a spiral valve into right cavum aortic and left cavum pulmocutaneous.

Bulbus arteriosus-
> This is the removed part from the ventricle- distal part.
> The synangium anteriorly divides into two branches. Each branch is named aortic trunk. Each aortic trunk is given three openings. They're carotid arch, systemic arch and pulmocutaneous arch.

Therefore, the correct option is A, conus arteriosus.

Note: The internal structure of the heart has two auricles, one ventricle, truncus arteriosus and therefore the valves stay the blood flowing in one direction. The two auricles are separated from one another by interauricular septum. Within the right auricle, near the septum there's a transverse oval opening called sinoauricular aperture. The blood enters into the right auricles through this aperture. This aperture is guarded by two lip-like flaps called sino-auricular valves. These valves allow the flow of blood towards right auricles but prevent backward flow of blood. In the left auricle near the septum there's a tiny low opening of vena pulmonalis which has no valves. The left auricle receives blood from lungs through pulmonary veins.