Question

Heart lacks sinus venosus in

• A. Fishes
• B. Mammals
• C. Amphibians
• D. Echinoderms

Answer 1

The correct option is B Mammals

Sinus venosus is a cavity which precedes the atrium. It is present between an enlarged region between the vena cava and the right atrium. It is formed by the union of the large systemic veins. It is a passage through which venous blood enters the heart in lower vertebrates. The mammals lack sinus venousus as the blood directly enters the right atrium.

So, the correct answer is option B.