THE ENDOSKELETON 



689 



copulae (Fig. 407). The two anterior arches are specialized and have 

 received special names, the first being the mandibular, the second the 

 hyoid arch, the others, in the region of the functional gills, being called 

 collectively gill or branchial arches. The number of these last varies 

 with the number of gill clefts, there being seven in the primitive sharks, 

 a smaller number in the higher groups, in which, with the loss of 

 branchial respiration, their form and functions may be altered. At first 

 all are clearly in the head region, but by the unequal growth of cranium 



Fig 408. 



A, B, C, Bones of early human skull to show their compound- nature. A, 

 occipital bone at birth showing the five elements of which it is composed. B, 

 sphenoid bone in an embryo of four months. C, temporal bone at birth, showing its 

 three components. Cartilage represented in black. (Redrawn from Sappey and 

 Hyman.) 



D, Diagram of skull of new born child. White areas represent bones of 

 intramembranous origin; dotted areas represent bones (not derived from branchial 

 arches ) of intracartilaginous origin ; black areas represent derivatives of branchial 

 arches. (Combined from McMurrich and Kollmann.) 



