Gastrointestinal tracts of a toad and salamander. A bony palate is present covering the roof of the buccal cavity. At the end of pyloric stomach a small constriction is present. Physiology of the Amphibia, vol. Pyloric stomach contains pyloric valve.
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The males of all modern reptiles, with the exception of tuatara , have functional copulatory organs. Unlike the penis of turtles and crocodiles, the copulatory organ of lizards and snakes is paired, with each unit being called a hemipenis.
The hemipenes of lizards and snakes are elongated tubular structures lying in the tail. Completion of the erection is brought about by blood filling the sinuses in the erectile tissue. Only one hemipenis is inserted into a female, but which one is a matter of chance.
Unlike the penis of mammals, the copulatory organs of reptiles do not transport sperm through a tube. The ducts from the testes, as already mentioned, empty into the cloaca, and the sperm flow along a groove on the surface of the penis or hemipenis. In general construction the eyes of reptiles are like those of other vertebrates. Accommodation for near vision in all living reptiles except snakes is accomplished by pressure being exerted on the lens by the surrounding muscular ring ciliary body , which thus makes the lens more spherical.
In snakes the same end is achieved by the lens being brought forward. The lens moves as a result of the pressure built up on the vitreous humour by contractions of muscles located at the base of the iris. The pupil shape varies remarkably among living reptiles, from the round opening characteristic of all turtles and many diurnal lizards and snakes to the vertical slit of crocodiles and nocturnal snakes and the horizontal slits of a few tree snakes.
Undoubtedly the most bizarre pupil shape is that of some geckos , in which the pupil contracts to form a series of pinholes, one above the other. The lower eyelid has the greater range of movement in most reptiles. In crocodiles the upper lid is more mobile. Snakes have no movable eyelids, their eyes being covered by a fixed transparent scale. Visual acuity varies greatly among living reptiles, being poorest in the burrowing lizards and snakes which often have very small eyes and greatest in active diurnal species which usually have large eyes.
Judging by the size of the skull opening in which the eye is situated, similar variation existed among the extinct reptiles. Extinct forms, such as the ichthyosaurs, that hunted active prey had large eyes and presumably excellent vision; many herbivorous types, such as the horned dinosaur Triceratops , had relatively small eyes and weak vision.
Colour vision has been demonstrated in few living reptiles. We welcome suggested improvements to any of our articles. You can make it easier for us to review and, hopefully, publish your contribution by keeping a few points in mind. Your contribution may be further edited by our staff, and its publication is subject to our final approval.
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Digestive and urogenital systems The digestive system of modern reptiles is similar in general plan to that of all higher vertebrates. Sense organs Sight In general construction the eyes of reptiles are like those of other vertebrates.
Previous page Circulatory system. Page 9 of Learn More in these related Britannica articles: Reptile s, of which there are few endemic families, have mainly Old World affinities. Those most likely to be seen include lizards of the agamid family, skinks a family of lizards characterized by smooth overlapping scales , crocodiles, and tortoises.
Endemic reptiles include girdle-tailed…. Although amphibian gastrulation is considerably modified in comparison with that in animals with oligolecithal eggs e. Such is not the case, however, in the higher vertebrates that possess eggs with…. The living reptiles belong to four orders: The reptile ear has many different forms, especially within the suborder Sauria lizards , and variations occur in…. Unlike lungfishes and amphibians, reptiles depend entirely on their lungs for respiration.
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Duke GE Alimentary canal: Avian Physiology, 4th edn, pp. Houdry J, Hermite AL and Ferrand R Changes in the digestive tract and feeding behaviour of anurian amphibians during metamorphosis. Luppa H Histology of the digestive tract. Reeder WG The digestive system. Physiology of the Amphibia, vol. Stevens CE Comparative physiology of the digestive system. Duke's Physiology of Domestic Animals, 9th edn, pp. Stevens CE and Hume ID Contributions of microbes in the vertebrate gastrointestinal tract to the production and conservation of nutrients.
Abstract The digestive systems of amphibians, reptiles, and birds share many characteristics with those of fish.