+------------------+-----------+---------+ | | Cervical. | Dorsal. | +------------------+-----------+---------+ | Vulture | 15 | 7 | | Eagle | 13 | 9 | | Cock | 14 | 7 | | Ostrich | 18 | 9 | | Swan | 23 | 10 | | Goose | 18 | 9 | | Duck | 15 | 9 | +------------------+-----------+---------+
In reptiles, the relation between the number of the cervical vertebræ and that of the dorsal is very variable; some serpents are devoid of cervical vertebræ, having only dorsal ones--that is, vertebræ carrying well-developed ribs.
+-------------------+-----------+---------+---------+ | | Cervical. | Dorsal. | Lumbar. | +-------------------+-----------+---------+---------+ | Crocodile | 7 | 14 | 3 | | Caiman | 7 | 12 | 5 | | Boa | 3 | 248 | 0 | | Python | 0 | 320 | 0 | | Viper | 2 | 145 | 0 | +-------------------+-----------+---------+---------+
Regarding the direction of the vertebral column in animals, in which the trunk is not vertical, it is evident that the spinous processes point upward, and that in comparing them with those of man they must be arranged so that the superior surface of the human vertebra will correspond to the anterior surface of that of the quadruped. Of the cervical vertebræ, the atlas and axis call for special notice. Apropos of the atlas, we find that it, in the human being, is narrower than the corresponding parts of the skull, and is therefore hidden under the base of the cranium (Fig. 2); in quadrupeds its width is equal to that of the skull, and sometimes exceeds, because of the great development of its wing-shaped transverse processes, that of the neighbouring parts of the head (Fig. 3). On this account those transverse processes often project under the skin of the lateral surfaces of the upper part of the neck.
[Illustration: FIG. 2.--SIZE OF THE ATLAS COMPARED WITH THE TRANSVERSE DIMENSIONS OF THE CORRESPONDING PARTS OF THE SKULL IN MAN.
1, Atlas; 2, mastoid process; 3, external occipital protuberance; 4, inferior maxilla.]
The axis is furnished on its anterior surface with the odontoid process, which articulates with the anterior (or inferior) arch of the atlas, according to the direction of the neck. The spinous process, flattened from without inwards, is more or less pointed; it is elongated from before backwards, so as partly to overlap the atlas and the third cervical vertebra.