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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]
The alignment of the vertebrae defines the shape of the human neck. [5] As the vertebrae bound the spinal canal, the cervical portion of the spinal cord is also found within the neck. Visceral compartment accommodates the trachea , larynx , pharynx , thyroid , and parathyroid glands .
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.
The transverse processes of mammals are homologous to the cervical ribs of other amniotes. In the whale, the cervical vertebrae are typically fused, an adaptation trading flexibility for stability during swimming. [28] [29] All mammals except manatees and sloths have seven cervical vertebrae, whatever the length of the neck. [30]
The average bird or mammal, both usually endotherms, have average brain-to-body ratios ten times larger than a typical ectotherm vertebrate. This has contributed to a common perception amongst researchers that mammals and birds share similar "advanced" cognitive characteristics as humans, while other vertebrates such as teleost fishes are more ...
The majority of mammals have seven cervical vertebrae (bones in the neck). The exceptions are the manatee and the two-toed sloth, which have six, and the three-toed sloth which has nine. [84] All mammalian brains possess a neocortex, a brain region unique to mammals. [85]
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.
Compared to the narrow vertebrae and the closely positioned zygapophyses of the pleurodires, the cryptodires’ vertebrae take on the opposite shape. Their cervical vertebrae are more distended, and their zygapophyses (processes that interlock adjacent vertebrae) are much more widely spaced—features allowing for a condition called ginglymoidy ...