The answer to the given question will be that the muscles that guard the entrances and exits of the internal passage are known as sphincter (circular muscles).
Due to their structure and controllability, skeletal circular muscles differ from their smooth muscle counterparts.
The muscularis mucosa, which is mostly found in the stomach, is composed of smooth muscle.
The longitudinal layer shortens the tract while the circular muscle layer in the muscularis externa prevents food from moving backward.The human body contains at least 50 or 60 different types of sphincters.
Some are quite small, like the many precapillary sphincters that line the circulatory system's blood vessels.
Lower esophageal sphincter (LES), pyloric sphincter (PS), ileocecal sphincter (ICS), and internal sphincter are the four different smooth muscle sphincters found in the GI system (IAS).
Hence, the answer is that the muscles that guard the entrances and exits of the internal passage are known as sphincter (circular muscles).
Most animals are well adapted to their biotic and abiotic conditions due to behavioural, physiological or structural adaptations that increase their chances of survival and reproduction. I looked it up for you
There are 6 base pair changes between species A and species B. Since we know the rate of change is 1 base pair every 4 million years, we know 6x 4 million is likely how long ago the species diverged. 6x 4 million = 24 million years