440 



distinction between the whales without a dorsal fin (Baleena) and those that have such fin 

 (Balcenoptera), in which the cervicals do not become anchylosed together. (See No. 2446.) 



Hunterian. 



2436. The skull of a foetal Southern Whale (Baleena australis, Cuv.). 



The plates of whalebone are about 1 70 on each side of the upper jaw. Each frontal is a 

 transversely elongated slender triangle, with its base at the frontal suture, which is a thick ver- 

 tical symphysis, and its apex at the superorbital ridge : the inferior angle of the base rests upon 

 the prefrontals and upon the sides of the expanded base of the vomer . The frontals take a very 

 small share in the formation of the cerebral cavity. Their cranial surface forms a very small 

 concavity at the back part of the base : a half-canal is continued forwards from the lower 

 angle of this surface into the nasal cavity. Almost the whole of the upper and outer surface of 

 the frontals is overlapped by the parietals and occipitals, leaving a very narrow exposed trans- 

 verse strip across the upper part of the skull. The anterior border of each frontal is joined 

 mesially with the nasal, next with the upper end of the premaxillary, and for the rest of its 

 extent with the maxillary bone, which is continued outwards to form the antorbital process. 



Purchased. 



2437. The cervical vertebrae of the same foetal Whale (Baleena australis). 



The neurapophyses of one side are disunited above from those of the other side, as they are 

 from the centrum below : a compressed diapophysis is sent off from the outer side of each ; it 

 is shortest and thickest in the atlas. The third and fourth neurapophyses have coalesced at 

 their upper part on the left side, and those of the last five vertebrae have coalesced on the right 

 side. The cortical portion of the centrum of the atlas is ossified, and forms a wedge-shaped 

 piece of bone, like the corresponding part in the Ichthyosaurus. The centrums of all the 

 cervical vertebra; have already coalesced by continuous ossification. 



Purchased. 



2438. The petrotympanic bones of the Southern Whale (Baleena australis}. 



Presented by George Bennett, Esq., F.Z.8. 



2439. The right petrotympanic bone of the Southern Whale (Baleena australis). 



Presented by J. Babington, Esq. 







2440. The opposing epiphyses of the centrums of two vertebrae of a young Whale 

 (Baleena}, with their intervening intervertebral substance. Hunterian. 



2441. One of the epiphyses, with an attached intervertebral cushion, of the centrum 

 of a vertebra of a larger Whale (Baleena}, 



This embryonic condition is not obliterated at any age in these gigantic aquatic Mammals, 

 which, being sustained in a medium of nearly their own specific gravity, have more need of 

 flexibility than of firmness in the vertebral column. As the same conditions influenced the 



