PART II. 



A. Comparative Anatomy and Histology. 



I. The Bones. 



IN common with the radiata, mollusca and arthropoda man 

 possesses a skeleton as framework for the muscular tissue, and 



__ __ ^j,juj. - in common with the vertebrata, 



??? 



" - ' .-,.* v an inner skeleton, which in the 



lower fishes and in the early 

 stages of development of the 

 other vertebrates is cartilagin- 

 ous in nature, in the later stages 

 osseous. 



The bones may be classified 

 as solid, porous and cellular. 

 They contain as inorganic con- 

 stituents basic phosphate of lime 

 together with fluorine, calcium, 

 carbonate of lime, phosphate of 

 magnesia and soluble salt ; as 

 organic, bone, cartilage and fat 

 (see Fig. 7). 



The number of bones in the 

 human body (see Fig. 8), when 

 the hyoid bone, the sternum and 

 the coccyx are each reckoned as 

 one only, is 223. The human 

 skeleton is so constructed that 

 wherever it corresponds to the 

 animal skeleton it still pos- 

 sesses certain essential differ- 

 ences which render the smallest 

 human bone immediately dis- 

 tinguishable from the corre- 

 52 



FIG. 7. Transverse section of the 

 metacarpal bone : a,, outer sur- 

 face ; b, inner surface ; c, medul- 

 lary canals ; d, lamellae ; e, bone 

 cavities with their ramifications. 

 Highly magnified. (From Thome, 

 Zoologie.) 



