680 MANUAL OF ZOOLOGY. 



and first two dorsal vertebrae are anchylosed to form a single 

 bone (" trivertebral bone " of Huxley), which articulates by a 

 movable hinge-joint with the remaining dorsal vertebras, which 

 are likewise anchylosed to form a kind of " tunnel or arched 

 bridge of bone." The last two lumbar vertebrae are also fused 

 with the sacral and caudal to form a continuous bony mass, 

 whilst the ilia are of enormous size. Numerous extinct forms 

 of genuine Armadillos have also been found in the Brazilian 

 bone-caves, one of them (Chlamydotherium) being as big as a 

 Rhinoceros. 



Lastly, the South American Myrmecophagida are represented 

 in the Brazilian cavern-deposits by the extinct Glossotherium. 



CHAPTER LXXI. 



SIRENIA AND CETACEA. 



.ORDER IV. SIRENIA. This order comprises no other living 

 animals except the Dugongs and Manatees, which have been 

 often placed with the true Cetaceans (Whales and Dolphins) in a 

 common order. There is no doubt, in fact, but that the Sirenia 

 present certain alliances to the Cetacea ; and though they are 

 to be regarded as separate orders, yet, from one point of view, 

 they may be considered as belonging to a single section, which 

 has been called Mutilata, from the constant absence of the 

 hind-limbs. 



The Sirenia agree with the Whales and Dolphins in their 

 complete adaptation to an aquatic mode of life (fig. 378) ; 

 especially in the presence of a powerful caudal fin, which differs 

 from that of Fishes in being placed horizontally, and in being a 

 mere expansion of the integuments, not supported by bony rays. 

 The hind-limbs are wholly wanting ; * and there is no sacrum. 

 The anterior limbs (fig. 379) are converted into swimming-paddles 

 or "flippers" The snout is fleshy and well-developed, and the 

 nostrils are placed on its upper surface, and not on the top of the 

 head, as in the Whales. Fleshy lips are present, and the upper 

 one usually carries a moustache. Ears are wanting. The skin 

 is covered with scattered bristles. The head is not dispropor- 

 tionately large, as in the true Whales, and is not so gradually 

 prolonged into the body as it is in the latter. There may be 



* All the Sirenians possess a rudimentary pelvis, and in the extinct Halt- 

 therium a small femur is present in addition. 



