A thin-walled, triangular chamber attached dorsally to heart of frog is known as

Options

A. Truncus arterisus
B. Sinus venosus
C. Atrium
D. Ventricle

Explanation

To answer the question, "A thin-walled, triangular chamber attached dorsally to the heart of a frog is known as," we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Anatomy of the Frog's Heart**:
- The frog's heart is a three-chambered organ consisting of one ventricle and two atria. It's important to recognize the structure and function of each part.

2. **Identify the Location of the Chamber**:
- The question specifies that the chamber in question is "thin-walled" and "triangular" and is attached dorsally to the heart.

3. **Visualize the Heart Structure**:
- By visualizing or referring to a diagram of the frog's heart, we can identify the various parts. The dorsal view will help in locating the triangular chamber.

4. **Recognize the Triangular Chamber**:
- In the dorsal view of the frog's heart, the triangular chamber that is observed is known as the **sinus venosus**. This chamber is responsible for receiving deoxygenated blood from the body before it enters the atrium.

5. **Eliminate Incorrect Options**:
- Other structures such as the atrium, ventricle, and truncus arteriosus do not match the description of a thin-walled, triangular chamber attached dorsally. The truncus arteriosus, for example, is located ventrally.

6. **Conclude the Answer**:
- Based on the identification and elimination of incorrect options, we conclude that the correct answer is the **sinus venosus**.

### Final Answer:
The thin-walled, triangular chamber attached dorsally to the heart of a frog is known as the **sinus venosus**.

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