Re: Do bats or other animals have hollow bones?

Tom,

Thanks for your question, it is interesting to compare the adaptations 
of bats and birds for flight.

Firstly, nearly all bones from all classes of vertebrate except fish are 
hollow when studied as decomposed or thoroughly cleaned specimens (and 
some fish bones are, too).  In other words, animals had discovered that 
tubes are structurally much more efficient than solid rods long before 
engineers did !  Bird bones are actually hollow (air filled) in the living 
animal, presumably for lightness, but air also circulates within their 
skeleton and may assist with respiration.

Mammal bones, while 'hollow' in that the solid parts of limb bones are 
tubular, are usually filled with fatty or "white" marrow, which is
different from the "red marrow" at the ends of the bones where blood cells
are manufactured.  The large quantity of fat within large mammal limb bones 
makes them very difficult to clean thoroughly.  Some parts of mammal bones, 
such as the sinuses in the skull, are air filled.

Bats have marrow in their bones, just like any other mammal, but the 
extreme narrowness of their bones means that the marrow-filled cavities are 
proportionally smaller than in other mammals, effectively giving them 
lighter bones than other mammals, an alternative adaptation for flight.