Reptiles

REPTILES (Reptilia), or reptiles, belong as a class to the subphylum of vertebrates and to the phylum of chordates. Three typical forms of R. can be distinguished: the lizard (long, slender body with two pairs of legs and a tail), the turtle (short, broad body with a well-developed external skeleton in the form of a shell), and the snake (long, narrow body without legs). The surface of the epidermis in R. strongly keratinizes; from time to time, molting occurs - the shedding of keratinized layers. The skin of R. is dry and almost completely devoid of glands. Such are the femoral pores of lizards, the musk gland of crocodiles, etc. Pigment cells are embedded in the coverings, and due to their contraction, the coloration of some R. quickly changes, taking on various tones (chameleon, agama, etc.). The skin skeleton of living R. is developed in crocodiles and especially strongly in turtles. The internal skeleton is bony, with little presence of cartilaginous tissue. The notochord is completely reduced and is preserved only in geckos. The spine of R., which have limbs, consists of cervical, thoracic, lumbar, sacral, and caudal sections. In limbless R., only the precoccygeal and caudal sections of the spine are differentiated. The number of vertebrae is particularly large in snakes (up to 422). The atlas and axis are present among the cervical vertebrae. In snakes, the ribs are movably connected to the vertebrae and contribute to crawling. The sternum is absent in snakes and turtles. The skull of R. is almost entirely bony with a single occipital condyle. There is a bony palate. The lower jaw is connected to the skull by means of the quadrate bone and os squamosum. There are one or two zygomatic arches. The girdles of the limbs are absent in snakes (rudiments of pelvic bones remain in pythons). The legs are constructed according to the type of terrestrial five-fingered limbs. The reduction of the limbs of R. begins with a decrease in the number of fingers. The muscles are more diverse in R., which have limbs and are devoid of an external shell. Many R. are capable of very fast and energetic movements. The digestive apparatus begins with the oral opening, leading into the oropharyngeal cavity, followed by the esophagus, stomach, small and large intestines, and cloaca. The tongue of R. is diverse in shape. It is particularly thin and mobile in snakes, is thrown to a considerable distance in chameleons, and serves rather as an organ of touch than of taste. The teeth are uniform or different in shape. In snakes, there are venomous canalicular or grooved teeth, connected with the excretory ducts of venom glands, which are homologues of the maxillary labial glands. There are also sublingual salivary glands. R. feed on various animals, some (turtles) are herbivorous. The ability of snakes to swallow prey much thicker than the snake itself is known. This depends on the connection of the lower jaws in front by an extremely stretchable elastic ligament and the great extensibility of the digestive canal itself. The accessory glands of the latter are the pancreas and the liver, which in snakes is very elongated in length. The lungs of R. are well developed, with a cellular inner surface, and the inner free cavity of the lungs in some R. (turtles) is almost completely lost. R. are cold-blooded. The heart in most R. has an incomplete septum between the right and left ventricle, but in crocodiles it is completely four-chambered. The number of arterial arches decreases; there are carotid and aortic arches. The venous sinus almost completely disappears. The anterior cardinal veins remain in the form of jugular veins, and the posterior cardinal veins disappear altogether. This is associated with the reduction of the primary kidney and its replacement by the secondary kidney. The ureters of R. open into the cloaca; a urinary bladder is present in turtles. In the female reproductive apparatus, the oviducts do not connect with the ovaries. The sperm ducts exist independently of the ureters. R. are oviparous or ovoviviparous. The brain is characterized by greater development of the cerebral hemispheres than in fish and amphibians. There are 12 pairs of cranial nerves. The sense organs are more diverse than in amphibians. In some R., there is a rudiment of the outer ear. Remarkable is the rudiment of the third parietal eye, remaining in some lizards and in the tuatara. Reptiles belong to Amniota, since the embryo during embryonic development is covered by embryonic membranes (amnion and allantois). Birds and mammals originated from reptiles. R. reached their greatest development in the Mesozoic. The vast majority of R. lead a terrestrial lifestyle, some live in fresh or sea water. R. are divided into subclasses: 1. Prosauria - first lizards (New Zealand tuatara). 2. Lepidosauria squamata - scaled reptiles: lizards (slowworm, monitor, gila monster, geckos, chameleons, etc.), snakes (see). 3. Crocodilia - crocodiles (Nile crocodile, caiman, etc.). 4. Chelonia, s. Testudinaria - turtles (Greek tortoise, marsh turtle, etc.). - The significance of R. for humans is diverse. Turtles are used for food; their horny plates and the skin of various R. are used for crafts. Predatory R., like crocodiles, are dangerous to humans, as they devour people who get into the water. Venomous snakes are of great importance (see Snake venom). Some R. are intermediate hosts of human helminths (e.g., snakes and Sparganum mansoni, which is the larva of Diphyllobothrium mansoni) and pentastomes Linguatulidae (e.g., Porocephalus armillatus in the lungs and trachea of pythons).