Question

Upward and downward movements of the throat during buccopharyngeal respiration by frogs are by which of the following set of muscles?
A. Mylohyoid and geniohyoid
B. Sternohyal and petrohyal
C. Retractor bulbi and levator bulbi
D. None of the above

Answer 1

Hint: Gaseous exchange in frogs occurs through the buccal and cutaneous path. It is the filling mechanism which helps frogs in the movement of their throat to push in air. They do not have ribs to force in the air to the lungs, so they do it with the help of their buccal cavity.

Complete answer: Amphibians have moist and well-vascularised skin which helps in gaseous exchange. Some small salamanders have no lungs and all gas exchanges take place through the skin surface except for a small contribution by the oral mucosa. While at rest, this process is their predominant form of breathing and frogs only fill the lungs occasionally. This is because the lungs that only adults have are poorly developed.
Invertebrates' filling of lungs can take place with the use of a pressure pump as in amphibians or a suction pump as in most reptiles, birds, and mammals.
A frog fills its mouth cavity and presses air into the lungs by elevating the floor of its mouth.
This filling mechanism helps a frog to take in repeated volumes of air continuously in sequence without letting air out. Amphibians do not have ribs so the floor of the buccal cavity is used to force air in and out of the lungs.
Frogs and toads modify second, third, and fourth visceral arches to produce a plate-like hyobranchial apparatus that lies in the floor of the oral cavity and is connected to the squamosal bone of the skull by betrayal muscle and sternum by sternohyoid muscle.
The contraction of these two muscles completes one breathing cycle.
So, the correct answer is “Option B”.

Note:
The buccopharyngeal respiration in frogs takes place through a set of muscles is Sternohyal and Petrohyal. Sternohyal is named so because it joins the sternum to the hyoid. Petrohyal is located outside the cavity of the mouth connecting the squamosal bone and hyoid.