62 CAUDAL VERTEBRA. [chap. 



In the Lemur ina the number of united vertebrae varies 

 from 2 to 5. 



In the Carnivora, as a general rule, there appears to be 

 but one true sacral vertebra, though one or more are ankylosed 

 to it behind, especially in the Bears and Seals, where as 

 many as 4 or 5 may be united by bone in old animals. In 

 the Dog there are usually 3 ankylosed vertebrae. 



In most Ungulata and Rodentia the sacrum consists of 

 one broad vertebra joining the ilia, and a series of narrow 

 ones, varying in number with age, gradually diminishing in 

 width, ankylosed to it behind. 



In the Beaver among Rodents, the Cape Anteater (Oryc- 

 teropus) among Edentates, and the Wombat among Marsu- 

 pials, the sacrum consists of numerous anky)csed vertebrae, 

 with widely- expanded transverse processes, which are longer 

 in the hindermost vertebrae, and nearly meet the ischia. 



In most other Edentata, as the Sloths, Anteaters, and 

 Armadillos, this modification is carried further, and the 

 transverse processes of the hinder pseudo-sacral vertebrae 

 form a complete bony union with the ischia, converting 

 into a foramen what is usually the sacro-sciatic notch. 

 In some of the Armadillos as many as 10 vertebrae are 

 thus most firmly fused together, and with the innominate 

 bones. 



In Marsupialia usually but one vertebra supports the iliac 

 bones, though another is commonly ankylosed with it. 



In the Monotremata, the Echidna has 3, and the Orni- 

 thorhynchus 2 ankylosed vertebrae. 



The Cetacea having no iliac bones, have no part of 

 the vertebral column specially modified into a sacrum ; but 

 in the Sirenia, the rudimentary ilia are attached by liga- 

 ment to the end of the transverse processes of one vertebra, 

 which may hence be regarded as sacral. 



