VERTEBRATA. 29 



five in the gallinaceae. The phalanges bear no proportion to the 

 size or number of the toes, being found to vary from one up to five. 



RECAPITULATION. 



1. There is more uniformity observed in the skeleton of birds, 

 than in any other of the vertebrated classes. 



2. The bones are white, thin, and brittle; in early life, filled 

 with a thin serous oil, which is subsequently removed to be replaced 

 by atmospheric air, especially in those of the high-flying kind. 



3. The bones are early and rapidly ossified, particularly those of 

 the head, thorax, and pelvis. This ossification also affects the ten- 

 dons of the muscles of the leg, sclerotic tunic of the eye, inferior 

 larynx, and the rings of the trachea. 



4. Arms adapted solely for flight ; legs for support. 



5. Head and neck long, for the purposes of prehension. 



6. The dorsal and sacral portions of the spine the most fixed. 



7. Cervical vertebras more numerous than in the mammalia; 

 occasionally, three times the number. 



MAMMALIA. 



The number of vertebrae contained in the spine, is very variable ; 

 but the human type is by far the most generally predominant. In 

 the cetaceae there is no distinction between lumbar, sacral, and 

 caudal vertebras ; and in the porpesse, there are sixty-six posterior 

 to the dorsal : these mammalia, however, have no pelvis. The 

 cervical vertebrae are uniformly seven throughout this class, not- 

 withstanding Cuvier imagined lie had found a solitary exception in 

 the neck of the ai, bradypus tridactylus; but it has been well as- 

 certained since, that what he conceived to be the two last cervical 

 vertebrae of this animal, have two rudimental ribs attached to them. 

 When we are reminded of the localities and habits of the sloth, 

 hanging from the branches of trees, and passing from bough to 

 bough, aided by the current winds, it becomes obvious why such a 

 provision should exist, of modifying the two superior dorsal verte- 

 brae, and of consigning to them the offices of cervical, rather than 

 infringe on a law which at present seems without an exception. 



The dorsal vertebrae range from twenty-three, as seen in the 

 unau, bradypus didactylus, to twelve, as presented by man, mice, 

 bats, rabbits, hares, and several apes. In the megatherium there 

 are sixteen, in the horse eighteen, and in the elephant twenty. 

 The lumbar vertebrae are generally seven; they vary, however, 

 there being two in the two-toed ant-eater, and nine in the lori. The 

 sacral vertebrae are seven in the mole ; in the vampyre bat, opossum, 

 and some apes, there is but a single sacral vertebra, the usual 

 number being three. The caudal vertebrae are four in man and 

 the ourang-outang; forty in the two-toed ant-eater; and in the 

 vampire bat they are altogether absent. 



