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ESSENTIALS OF ZOOLOGY 



The epihyal is connected to the hyomandibular by a ligament, 

 and the hypohyal to the first hypobranchial. The branchial 

 arches are divided up into four segments each, pharyngo-, epi-, 

 cerato-, and hypo-branchials. It will be observed that the 

 ventral elements of the first and the fifth arches fuse with their 

 neighbours, and that the fourth and fifth arches fuse with one 

 another dorsally on each side. The fifth arch also is attached 

 to the pectoral girdle (fig. 80). The spiracle lies in front of 



Mesop. 

 Coracoid Scap. Propterygium 



Fin ray 



Metapterygium 

 Pubic process 

 Iliac process 

 Metapterygium 



Fin rays 



FIG. 81. Raia. Dorsal view of the pectoral and the pelvic girdles. 



the hyoid, the first branchial cleft between the hyoid and the 

 first branchial arch, and so on. 



In addition to the cartilages mentioned, there are others 

 which are developed in regions requiring extra support or in 

 positions which suggest they may be of interest as rudimentary 

 evidences of pre-existing arches or structures. Such are the 

 labial cartilages developed in relationship to the upper and 

 lower jaws, the spiracular cartilage developed in front of the 

 hyomandibular. The extrabranchial cartilages appear to be 

 rather Elasmobranch than historical in their nature. 



The paired fins are heralded by the appearance of horizontal 

 and practically continuous ridges of the sides of the body of 



