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An anal fissure is a break or tear in the skin of the anal canal. Anal fissures may be noticed by bright red anal bleeding on toilet paper and undergarments, or sometimes in the toilet. If acute they are painful after defecation , [ 1 ] but with chronic fissures, pain intensity often reduces and becomes cyclical.
However, most tetrapod species today are amniotes, most of which are terrestrial tetrapods whose branch evolved from earlier tetrapods early in the Late Carboniferous. The key innovation in amniotes over amphibians is the amnion , which enables the eggs to retain their aqueous contents on land, rather than needing to stay in water.
Peto's paradox is the observation that, at the species level, the incidence of cancer does not appear to correlate with the number of cells in an organism. [1] For example, the incidence of cancer in humans is much higher than the incidence of cancer in whales, [2] despite whales having more cells than humans.
[18] [19] Tetrapods can be divided into four classes: amphibians, reptiles, birds and mammals. Marine tetrapods are tetrapods that returned from land back to the sea again. The first returns to the ocean may have occurred as early as the Carboniferous Period [ 20 ] whereas other returns occurred as recently as the Cenozoic , as in cetaceans ...
Anal cancer is a cancer which arises from the anus, the distal opening of the gastrointestinal tract. [1] Symptoms may include bleeding from the anus or a lump near the anus. [ 1 ] Other symptoms may include pain, itchiness, or discharge from the anus. [ 1 ]
The tetrapods evolved from the lobe-finned fishes about 395 million years ago in the Devonian. [23] The specific aquatic ancestors of the tetrapods, and the process by which land colonization occurred, remain unclear, and are areas of active research and debate among palaeontologists at present.
In tetrapods, a mostly terrestrial clade evolved from lobe-finned fish, many pharyngeal arch elements are lost, including the gill arches. In amphibians and reptiles , only the oral jaws and a hyoid apparatus remains, and in mammals and birds the hyoid is simplified further to support the tongue and floor of the mouth .
Evolution of tetrapods (3 C, 14 P) R. Reptiliomorphs (5 C, 11 P) T. Tetrapod taxa (3 C) Pages in category "Tetrapods" The following 4 pages are in this category, out ...