Multiple choice

Sinus venous is absent in

  1. mammal

  2. reptile

  3. aves

  4. fish

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Sinus venosus, a fetal heart structure that returns blood to the right atrium, is absent in mammals. In mammals, this function is taken over by the superior and inferior vena cava. It persists in other vertebrates like fish, reptiles, and birds.