98 



HITCHCOCK'S ANATOMY 



considerably ossified. This is especially true of those in 

 the leg. 



211. Birds Bones are hollow. — The bones of birds are 

 more or less hollow internally, devoid of marrow, and per- 

 meated by air. Hence they are provided with openings con- 

 nected with the respiratory apparatus through which the air is 

 brought into them. As a general rule the capacity and extent 

 of these openings throughout the skeleton depends on the size 

 of the bird, and its powers of flight, since small though rap- 

 idly flying birds have few hollow bones ; in larger and higher 

 flying species, however, they are numerous. In the Apteryx 

 of New Zealand there is the greatest want of these cells. This 

 bird has no wings, but can run and even burrow in the earth 

 very rapidly. Those bones which convey the air, differ from 

 all others in appearance by their whiteness and more com- 

 pactly cancellated or cellular structure. 



OSTEOLOGY OF REPTILES. 



212. Number of Vertebrae in Reptiles, — The Vertebrae 

 of Reptiles vary exceedingly in number. " For whilst in 

 the tailless Batrachia only nine or eight cervical vertebrae are 

 counted, some serpents have full 300." Those of Batrach- 

 ians have long transverse processes. 



213. Ribs; Use of Ribs to Serpents. — " In the serpents 

 the ribs are both very numerous and very movable ; where 

 they cease the tail begins ; here the Caudal vertebrae may be 

 distinguished from the other vertebrae of the trunk, whilst all 

 distinction of dorsal and lumbar vertebrae fails. " They are 



211. Why are birds' bones usually hollow and more or less occupied by cavities? 

 212. What is the number of vertebrae in Reptiles? 213. Give the number of ribs in 

 Reptiles. How do they differ from those of quadrupeds ? Of what service are they to 

 the animal ? 



