158 



HISTORY OF THE HUMAN BODY 



FIG. 41. Morphology of the visceral skeleton. 



(A) Selachian. (B) Amphibian. (C) Sauropsidan. (D) Mammal. 

 In all the figures the visceral arches are designated by Roman numerals; in the 

 case of the first two the dorsal and ventral segments are further designated by ex- 

 ponent letters (d and v). Other designations are, Ib, labial cartilage; s, spiracular 

 cartilage; o, operculum. In arch VII the . arytaenoid and tracheal cartilages are 

 designated by the exponents a and b, respectively. The designations for the stapes 

 represent an interpretation at variance with the one given in the text, but formerly 

 widely accepted. 



