vi.] MONOTREMATA. 77 



Chevron bones are generally present in the tails of all the 

 Marsupials, except the Wombat and Koala. In the Thylacine 

 they are few, and comparatively rudimentary. 



The tails of the two forms composing the order 

 MONOTREMATA differ considerably. 



The Echidna has 12 caudal vertebrae. These have no 

 hypapophyses, but there are two single median chevron 

 bones near the middle of the tail, more like the lumbar 

 subvertebral ossicles of the Mole than ordinary chevron 

 bodies. The Ornithorhynchus has 20 or 21 caudal vertebrae, 

 with single median hypapophyses, no chevron bones, and 

 wide transverse processes which increase in length towards 

 the middle of the tail, being shortest near the sacrum and 

 end of the tail. 



The following Table, showing the number of vertebrae in 

 a very large series of Mammals, is mainly taken from the Cata- 

 logue of the Museum of the Royal College of Surgeons of 

 England. 1 Those distinguished by an asterisk (*) are from 

 the collection of the University of Cambridge, and have been 

 added to make the list still more complete. The + after the 

 number of the caudal vertebrae indicates that the termina- 

 tion of this region (as too often happens with mounted 

 skeletons) was defective. The others are presumed to be 

 complete or very nearly so. 



In compiling this list the following rules have been 

 observed : The cervical vertebrae are those in front of the 

 first which bears a rib directly articulating with the sternum. 

 The thoracic or dorsal vertebrae are those which bear 



1 Catalogue of the Specimens illustrating the Osteology and Dentition 

 of Vertebrated Animals recent and extinct, contained in the Museum of 

 the Royal College of Surgeons of England, part ii. Class Mammalia, other 

 than Man, by W. H. Flower, assisted by J. G. Garson. London, 1884. 



