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The vertebral transverse processes of mammals are homologous to the cervical ribs of other amniotes. [citation needed] Most mammals have seven cervical vertebrae, with the only three known exceptions being the manatee with six, the two-toed sloth with five or six, and the three-toed sloth with nine. [2] [3]
Two-toed sloths are unusual among mammals in possessing as few as five cervical vertebrae, which may be due to mutations in the homeotic genes. [27] All other mammals have seven cervical vertebrae, [28] other than the three-toed sloth and the manatee.
Xenarthrans also tend to have different numbers of vertebrae than other mammals; sloths have a reduced number of lumbar vertebrae with either more or fewer cervical vertebrae than most mammals, while cingulates have neck vertebrae fused into a cervical tube, with glyptodonts fusing thoracic and lumbar vertebrae as well. [1]
During craniocaudal folding, it assumes a position cranial to the developing heart at the level of the cervical vertebrae. [1] During subsequent weeks the dorsal end of the embryo grows much faster than its ventral counterpart resulting in an apparent descent of the ventrally located septum transversum. At week 8, it can be found at the level ...
The cervical spine, found in all mammals, consists of seven vertebrae which, however, are reduced or fused. This fusion provides stability during swimming at the expense of mobility. The fins are carried by the thoracic vertebrae, ranging from nine to seventeen individual vertebrae.
The number of vertebrae in a region can vary but overall the number remains the same. In a human spinal column, there are normally 33 vertebrae. [3] The upper 24 pre-sacral vertebrae are articulating and separated from each other by intervertebral discs, and the lower nine are fused in adults, five in the sacrum and four in the coccyx, or tailbone.
A mammal (from Latin mamma 'breast') [1] is a vertebrate animal of the class Mammalia (/ m ə ˈ m eɪ l i. ə /).Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three middle ear bones.
The Nomina Anatomica Avium (NAA) terminology instead uses the term thoracic vertebrae. In mammals, the term thoracic vertebrae refers only to the rib-bearing vertebrae of the chest, while the vertebrae of the lower back, which lack ribs, are referred to as lumbar vertebrae. This subdivision of the dorsal vertebral column is not applicable in ...