464 DE. H. WOODWAKD 0^ Als" ALMOST 



size and their wider and longer transYerse processes, be considered 

 lumbar and sacral, and the 21 following vertebrse as caudal ; about 

 6 or 8 of the most anterior of the latter had small chevron-bones or 

 haemal arches attached to them in the St, Petersburg specimen. 



The transverse processes in the caudal series are much smaller, 

 thicker, and shorter, and are directed obliquely backwards. 



Variation in form of tJie Centra in the Vertebral Column. — There 

 is a marked change in the form and size of the neural arch and the 

 centrum of the several vertebrae in the sjjinal column, from before 

 backwards. The anterior dorsal vertebrae have each a small com- 

 pressed centrum, much broader than deep ; the neural arch is 

 triangular, the neural spine erect. 



Prom the 5th to the 8th dorsal the centra -are longer and cordi- 

 form, and the neural canal is smaller and more rounded : the neural 

 spine bends backwards, and the zygapophyses are more prominent. 

 . The lumbar vertebrae are much dilated laterally, the centra being 

 nearly three times as broad as deep. The neural canal is reduced 

 in size, and the neural spine is moderately large ; but the transverse 

 processes are very flat, long, broad and straight, being in relation 

 to the centrum as 5 to 1. 



The centra of the caudal vertebrae are rounder, the transverse 

 processes are short and stout and bent backwards ; the neural canal 

 is reduced to a very small size, and the neural spine graduaEy 

 disappears. 



The earlier caudals have short Y-shaped chevron -bones or haemal 

 arches. 



The 11th to 16th thoracic or dorsal vertebrae have irregularly 

 developed hypapophyses on the ventral surface of their centra. 



There are 19 pairs of ribs in Bhytina, probably not more than 

 two pairs of which were articulated to the sternum. The 1st and 

 2nd pairs are short and much compressed laterally, the third and 

 following are round and very massive, and increase in curvature and 

 length up to the 12th, when they gradually become shorter and less 

 curved, the 19th being quite rudimentary. 



This large number of rib-bearing vertebrae in the Sirenia is only 

 equalled in Elejohas and Rhinoceros, and only exceeded in Dendrohyrax 

 (which has 22 costal vertebrae), thus affording another point of 

 analogy in Rhytina to the TJngulata*. 



The ovoid visceral cavity thus enclosed within the bony walls of 

 the ribs is of vast dimensions ; and one realizes readily the statement 

 that a full-grown male, covered with its integument and flesh, 

 weighed as much as 3|^ tons. 



Habits of Khytina, &c. — The Sirenia pass their whole life in the 

 water, being denizens of the shallow bays, estuaries, lagoons, and 



* The teeth in Manatus and Halitkeriv.m approach in form to the molars in 

 Hijypo'potamus, Mastodon, and the Suid«. 



Dr. Murie strongly insists upon the dermal characters as oiFering a Tery close 

 resemblance between Manatus and Elephas. The short (rudimentary) nasal 

 bones and the prolonged premaxillaries, with their tusk-like incisors, afford 

 further points of resemblance with the Proboscidea. 



