88 



COMPARATIVE MORPHOLOGY OF VERTEBRATES 



geal jaw. The upper elements of the other arches are frequently expanded, 

 bear teeth, and are called epipharyngeal bones. 



Fig. 89. — Pterygoids, suspensorium and operculum of mackerel {Scomber) after 

 AUis. enp, entopterygoid; ep, ectopterygoid; hm, hyomandibular; to, interoperculum; 

 mtp, metapterygoid; op, operculum; pi, palatine; po, preoperculum; q, quadrate; sop, 

 suboperculum; sy, symplectic. 



Fig. 90. — Skull oi Lepidosiren, after Bridge, an, angulare; ap, antorbital process; 

 ch, ceratohyal; cr, cranial rib; de, dermal ethmoid; dee, dermal ectethmoid; eo, exocdpital; 

 tp, frontoparietal; hr, hyoidean ribs; mk, Meckel's cartilage; na, first neural arch; nc, 

 nasal capsule; nsp, neural spine; pq, pterygoquadrate; sc, sagittal crest of frontoparietal; 

 sp, splenial; sq, squamosal; i-io, nerve exits. 



Dipnoi. — In the three existing genera (fig. 90) the skull is comparatively 

 uniform, but the fossils, beginning in the Devonian, have a wide range of struc- 

 ture. In the former the cavity of the chondrocranium extends to the ethmoid 



