In the heart of frog, which of the following is considered as pacemaker ?

Options

A. Pylangium
B. Synangium
C. Sinuauricular node
D. Truncus arteriosus

Answer

### Step-by-Step Solution

1. **Understanding the Question**: The question asks about the pacemaker of the frog's heart. The pacemaker is the part of the heart that initiates the heartbeat.

2. **Identifying the Options**: The options provided are:
- Phalangium
- Synangium
- Sinoauricular node
- Truncus arteriosus

3. **Defining the Pacemaker**: In amphibians, including frogs, the pacemaker is responsible for generating electrical impulses that trigger heart contractions.

4. **Locating the Pacemaker in Frogs**: In frogs, the pacemaker is known as the **sinoauricular node**, which is also referred to as the **sinus venosus**. This structure is located between the vena cava and the right atrium of the heart.

5. **Understanding the Heart Structure**: The frog's heart is three-chambered, consisting of two atria and one ventricle. The sinoauricular node plays a crucial role in regulating the flow of blood from the vena cava into the right atrium via the sinus venosus.

6. **Conclusion**: Based on the information, the correct answer to the question is the **sinoauricular node** (or sinus venosus), as it functions as the pacemaker in the frog's heart.

### Final Answer
The pacemaker in the heart of a frog is the **sinoauricular node** (sinus venosus).

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