460 



THE VERTEBRATE SKELETON. 



of the skull between the squamosal, supra-occipital and exocci- 

 pital, there is a wide vacuity in the cranial wall, partially filled 



.-5 



FIG. 92. LATEBAL VIEW OF THE SKULL OF Rhytina stelleri x % 

 (Brit. Mus.) 



7. 



frontal, 

 parietal, 

 zygomatic process 



squamosal. 

 squamosal. 

 exoccipital. 

 occipital condyle. 



pterygoid process of the ali- 



sphenoid. 

 of the 8. jugal. 



9. premaxilla. 



10. angle of the mandible. 



11. maxilla. 



up by the very large periotic, which is aiikylosed to the tym- 

 panic, but is not united to any other bones of the skull. The 

 foramen lacerum medium is confluent with the foramen lacerum 

 anterius, and the two together form an enormous vacuity on 

 the floor of the skull, bounded chiefly by the exoccipital, basi- 

 occipital, alisphenoid and squamosal. The jugal (fig. 92, 8) is 

 large and in Manatus sends up a strong process, which nearly 

 or quite meets the postorbital process of the frontal, completing 

 the orbit. In the other Sirenia the orbit is completely confluent 

 with the very large temporal fossa. The lachrymal in Manatus 

 is very small, but is larger in Halicore. The premaxillae (fig. 

 92, 9) are large, but smaller in Manatus than in the other 



