It is worthy of notice that in birds the number of the cervical vertebræ is not constant, as in mammals; they are more numerous than the dorsal. These latter are almost always joined to one another by a fusion of their spinous processes; the two or three last vertebræ are similarly united to the iliac bones, between which they are fixed. The dorsal vertebræ thus form one piece, which gives solidity to the trunk, and provides a base of support to the wings, for the movements of flying. There are, so to speak, no lumbar vertebræ, the bones of that region, which cannot be differentiated from the sacrum, having coalesced with the bones of the pelvis.
Vertebræ.
| 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.
Vertebræ.
| Cervical. | Dorsal. | Lumbar. | |
| Crocodile | 7 | 14 | 3 |
| Caiman | 7 | 12 | 5 |
| Boa | 3 | 248 | 0 |
| Python | 0 | 320 | 0 |
| Viper | 2 | 145 | 0 |
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.