84 
the bradypus 9. Caudal in man, including ossa in- 
nominata, 4, lumbar 7; in all 30. The caudal in 
monkeys vary from 20 to 30, in myrmecophaga di- 
dactyla amount to 40, in the porpoise to 66. 
In birds, the owl has of vertebrae 12 cervical, 
8 dorsal, 12 sacrolumbar, 8 caudal; in all 40. In 
small hopping birds the sacro-lumbar are 8 or 9. In 
the heron (ardea cinerea) there are 18 cervical, 7 
dorsal, 10 sacro-lumbar, 7 caudal; in all 42. The 
sacro-lumbar in ostriches are 20. ‘The dorsal ver- 
tebree are moveable in the ostrich and cassowary, not 
in other birds. The bones of all birds are hollow, 
and admit a great quantity of air, which is heated, 
and therefore lighter than the atmosphere: which 
circumstance, in running as well as in swimming and 
flying, facilitates motion by imparting buoyancy. 
This, however, is not the case in the bones of bats, 
so that the connection of the bones with air-vessels 
in birds doubtless is adapted to an ulterior, probably 
to a double purpose. | 
In the class mammalia, as well as that of birds, we 
see in this case not only a difference of plus and 
minus, but also a tendency amongst some of each 
class to exhibit an affinity with the other proximate 
class. Several analogies between mammalia and 
aves are noticed by Carus". “In the sloth the 
greater number and consolidation of the sacral ver- 
tebre and their breadth remind us of the sacrum of 
birds.” 
«© The vertebral column of birds so far resembles 
» Pag. 194. 
