Snakes belong to the group of reptiles that are the first terrestrial vertebrates, and their appearance was recorded during the Triassic. Adaptation on land was made possible by the appearance of a waterproof amniotic egg. Another important adaptation was the development of skin with scales that protect them from adverse external conditions and dehydration. However, the skin cannot keep up with the growth and changes occur. In the case of a snake, it is changed in one piece and snakes, before the change takes place, become restless due to poor eyesight. Snakes have developed a number of senses that make it easier to spot, capture and manipulate prey. Certain families of snakes have developed special organs that are sensitive to heat. They use them to see the infrared radiation of their prey and this enables them to hunt even in the dark. Sensations of the ground vibrations they receive are transmitted via the lower jaw, quadrate bone and stirrup to the internal mechanoreceptors in the lower jaw. Chemical information is received by snakes through the vomernasal or Jacobson's organ at the tips of the long forked tongue. In Jacobson's organ, the receptors react to odor particles collected by pallor. The importance of vision in snakes varies, species that prefer open habitats have far more sensory cells than those that live on ground covered with dense vegetation. In snakes, a nervous system develops unlike its ancestors. The cerebrum is made up of two hemispheres and has a developed cerebral cortex, but no sulcus and cerebral gyrus. The cerebellum in snakes is not sufficiently developed and is elongated and narrow. The spinal cord has a similar structure to that of mammals.