Digestive and nervous systems of amphibians and their senses

Digestive system

The digestive system is represented by the digestive tract and glands.
Digestive tract: mouth – pharynx – esophagus – stomach – intestines (thin and thick) – cloaca.
In the oropharyngeal cavity, the ducts of the salivary glands, nostrils (choanae), and the openings of the Eustachian tubes (middle ear) open. It also contains the tongue, which is attached by the front end to the lower jaw.
The esophagus is short.
The intestine is divided into thick and thin. The large intestine ends in a cloaca.
Digestive glands – Secrete substances (enzymes) necessary for the digestion of food.
Salivary glands – secrete saliva;
liver – secretes bile, which accumulates in the gallbladder;
pancreas – secretes pancreatic juice.

Nervous system

The nervous system is formed by the brain and spinal cord, as well as peripheral nerves.
In the brain of amphibians, the anterior section is more developed than in fish. The cerebellum and midbrain are relatively poorly developed, since amphibians are inactive, their movements are monotonous.

Sense organs

The senses are adapted to a terrestrial lifestyle.
The eyes are equipped with two movable eyelids: the upper – mobile leathery – and the lower – transparent blinking membrane. The eyelids have evolved. They protect the eyes from dust, dirt and drying out. Amphibians see farther than fish, because the lens has the shape of a lens (convex).
In the organs of hearing (in addition to the inner ear, which was still in fish), the middle ear appears, delimited from the external environment by the eardrum. In the middle ear of amphibians, there is only one auditory ossicle (stapes).
Amphibians were the first vertebrates to make sounds. To amplify sounds, males use special bags – resonators.
The olfactory organs are represented by olfactory capsules associated with the nostrils.

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