Saihets-hezur: berrikuspenen arteko aldeak
Ezabatutako edukia Gehitutako edukia
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45. lerroa:
* <u>Saihetsezur zeharkako arantza lotailua</u>: Saihets lepotik maila bereko ornoaren zeharkako irtengunera.
=== Saihetsak animalietan ===
Arrainek, normalean, 2
In fish, there are often two sets of ribs attached to the vertebral column. One set, the '''dorsal ribs''', are found in the dividing septum between the upper and lower parts of the main muscle segments, projecting roughly sideways from the vertebral column. The second set, of '''ventral ribs''' arise from the vertebral column just below the dorsal ribs, and enclose the lower body, often joining at the tips. Not all species possess both types of rib, with the dorsal ribs being most commonly absent. Sharks, for example, have no dorsal ribs, and only very short ventral ribs, while lampreys have no ribs at all. In some teleosts, there may be additional rib-like bones within the muscle mass.
Tetrapods, however, only ever have a single set of ribs which are probably homologous with the dorsal ribs of fishes. In the early tetrapods, every vertebra bore a pair of ribs, although those on the thoracic vertebrae are typically the longest. The sacral ribs were stout and short, since they formed part of the pelvis, connecting the backbone to the hip bones.
In most subsequent forms, many of these early ribs have been lost, and in living amphibians and reptiles, there is great variation in rib structure and number. For example, turtles have only eight pairs of ribs, which are developed into a bony or cartilagenous carapace and plastron, while snakes have numerous ribs running along the full length of their trunk. Frogs typically have no ribs, aside from a sacral pair, which form part of the pelvis.
In birds, ribs are present as distinct bones only on the thoracic region, although small fused ribs are present on the cervical vertebrae. The thoracic ribs of birds possess a wide projection to the rear; this '''uncinate process''' is an attachment for the shoulder muscles. Usually dogs have 26 ribs. Mammals usually also only have distinct ribs on the thoracic vertebra, although fixed cervical ribs are also present in monotremes. In marsupials and placental mammals, the cervical and lumbar ribs are found only as tiny remnants fused to the vertebrae, where they are referred to as '''transverse processes'''. In general, the structure and number of the true ribs in humans is similar to that in other mammals. Unlike reptiles, caudal ribs are never found in mammals
=== Irudi gehigarriak ===
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55 ⟶ 64 lerroa:
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=== kanpo loturak ===
{{Commonskat}}
{{Anatomia zirriborroa}}
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