THE BONES AND JOINTS. 



The consideration of the differences in form, number, and histo- 

 logical structure, which the parts of the skeleton present during- 

 the various stages of development does not fall within the scope of 

 this book : we have here but to deal with the adult frog. 



The skeleton is made up of histologically different materials ; 

 these are: — (i) bone, (2) hyaline cartilage, and (3) so-called cal- 

 cified cartilage. Concerning the last it is necessary to make 

 some observations. I have chosen for it the name calcified car- 

 tilage in place of the more usual names 'cartilaginous bone^ or 

 'primordial ossification,^ as by this term its nature appears to 

 be expressed without any ambiguity ^ : it is hyaline cartilage 

 in which calcareous particles have been deposited to a greater or 

 less extent : in the fresh state it has the appearance of moderately 

 firm cartilage ; when dry it becomes opaque and white, like the 

 calcareous crusts on the cartilages of the Plagiostomata. The cal- 

 careous material is deposited in the cartilage in finer or coarser 

 granules ; after removal of the lime by means of acids, the cartila- 

 ginous structure becomes apparent although not so perfectly as in 

 unchanged cartilage. 



This calcified cartilage is widely distributed in the frog^s skeleton : 

 very many parts, which in higher animals consist only temporarily 

 of this substance during the transition from cartilage to bone, are in 

 the frog formed of it throughout life. It is especially well-marked 

 in the epiphyses of the long bones in the hand and foot, in the 

 bones of the shoulder-girdle, etc. To avoid repetition later on I will 

 briefly describe it as found in the first-mentioned situation. Dugès '^ 

 has described its external appearance, while Bruch^ has made us 



^ Compare Miiller, Zeit. f. wissen. Zoolog., Vol. IX. 



^ Dugès, Recherches sur l'ostéologie et la myologie des batraciens à leurs différents 

 âges, p. 116. 



^ Bruch, Beitriige zur Entwicklungsgeschichte des Knochensystems. Schweiz. 

 Denkschriften, p. 11 S. 



