iv.] CETACEA. 43 



processes. In a specimen of Manatus senegalensis, in the 

 Museum of the College of Surgeons, the second and third 

 are ankylosed by their bodies, and the neural arches of most 

 of the others are widely open above. In the skeletons of M. 

 americanus, in the same museum, the vertebrae are all free, 

 and the arches, though slender, are complete, and with very 

 slightly developed spinous processes. In a specimen of M. 

 americanus in the Museum of Cambridge the axis and atlas 

 have large neural spines ; the vertebrarterial canal is incom- 

 plete in the 2nd, 3rd and 4th vertebra, wanting in the 5th, 

 but complete in the 6th which carries a distinct movable 

 cervical rib. 



In the Cetacea the seven cervical vertebrae usually found 

 in the Mammalia are always present, though often so short 

 and blended together, that it is not easy at first sight to re- 

 cognise their existence. In some genera of both sub-orders 

 all the vertebrae are free, though never allowing of much 

 motion between them ; but more commonly certain of them 

 are firmly united together by bone. Even where the atlas 

 and axis are separate the odontoid rarely forms a distinct 

 process (it is most distinct in Platanista], but still it is devel- 

 oped from an ossific centre of its own, as in other Mammals. 



Among the Mystacoceti^ in the Right Whales (genus 

 BalcEiia] the whole of the seven cervical vertebrae are usually 

 united into one mass by their bodies, though sometimes the 

 seventh is free. The arches are also more or less united 

 above, though generally not in a continuous mass. Small 

 slit-like openings between the narrow pedicles of the arches 

 permit the exit of the cervical spinal nerves, and in the adult 

 condition afford the only indications by which the number of 

 the united vertebras can be ascertained. Already before 

 birth most of the bodies have coalesced, and it is even 

 doubtful whether they ever exist in a separate condition. 



