430 



ANATOMY OF VERTEBRATES. 



Sea-cow' {Rlujtina horealis, 111.), last observed in the arctic seas 

 off the shores of Bering's Island: the miocene extinct genus 

 {Halitlieriuiii) has left its remains in southern Europe. 



A. Vertebral Column. — In the Dugong, fig. 292, there are 

 7 cervical, c, 19 dorsal, D, and about 26 lumbo-caudal vertebrae, 

 L, S, CD. To the 29th vertebra, counting from the skull, the 

 pelvic arch is suspended, characterising it as a sacral one, s, and 

 lea\dno- two lumbars in advance, the transverse processes of which 

 long retain the suture indicative of their pleurapophysial part. 

 The second vertebra, beyond the sacral, first supports a h^mal 

 arch, and this is continued to the fourteenth and fifteenth of the 

 caudal series, which, if counted from the sacrum, would include 

 about twenty-four vertebrae. Fig. 291 gives the characters of 

 the transitional vertebras between the trunk and tail, especially 

 as afforded by modifications of the haemal arch. In the posterior 

 dorsal vertebrae, the pleurapophysis, 79/, is the sole ossified 

 element of the haemal arch; it progressively shortens in the 



291 



Dorsal, lumbar, sacral, caudal, vertebrfe, Ealicore. 



16th, 1, 17th, 2, and 18th, 3, vertebrae, retaining its mobility; 

 and, in the 19th, A, it shortens suddenly, but usually with more 

 extended ossification in the sclerous basis of the rib than is shown 

 in the figure. In the vertebra, B and C, the pleurapophysis, 

 besides being short, becomes confluent with the centrum, as a 

 'transverse process,' and characterises them as Mumbar.' The 

 sclerous or tendinous continuations of the pleurapophyses into the 

 abdominal muscles are indicated by dotted Knes. In the ver- 

 tebra D, the ossification which extends the pleurapophysis, pi, 7, 

 beyond the part, d, representing the transverse process, retains 

 a ligamentous union therewith, and represents the ^ ilium:' a 



