XII.] 



SIRENIA. 



199 



have skulls constructed on a very peculiar type, though with 

 some affinities both to the Ungulata and the Proboscideia. 

 Many of the special modifications are adaptations to their 



ExO 



Fig. 64. — Section of the skull ot an African Manati (Manatus senegalensis), \ 

 PMx premaxilla ; Vo vomer; Mx maxilla; Fr frontal ; ET ethmoturbinal ; 

 ME mesethmoid ; Fr frontal ; Pa parietal ; Sq squamosal ; SO supraoccipital ; 

 ExO exoccipital ; rer periotic ; BO basioccipital ; Ty tympanic ; AS alisphenoid ; 

 BS basisphenoid ; PS presphenoid ; Pt pterygoid ; PI palatine ; Mx maxilla ; 

 cp coronoid process of mandible; cd condyle; a angle; s symphysis; sk stylo- 

 hyal ; bh basihyal ; th thyrohyal. 



aquatic mode of life, and it is in these alone that they 

 present any resemblances to the Cetacea. 



— 



