trabecula and 

 orbital cartilage 



lateral otic wall 



occipital arch 



_notochord 



foramen apical' 



nasal tectum 



Meckel's cartilage 



^^;^^_3^eratobranchials MM 

 copula -^cerotohyal 



quadrate cartilage 



B 



Meckel's cartilage 



paranasal cartilage 



anterior 

 cupola, 



■^otic process 

 ■X ^ascending process 



sclerotic cartilage 

 otic capsule 



palatine division of VII 



Vil 



endolymphatic foramen 

 otic capsule. 



synotic tectum 



Meckel's cartilage 



pterygoid process 

 ascending process 



otic process of 

 quadrate cartilag 



stapes 

 operculum 



perilymphatic fenestrae 



occipital arch 

 notochord 



ascending process 



pterygoid process 



Figure 4-19. Development of chondrocranium in Ambystomo, a salamander, and Sa/amandra. 

 A head skeleton 9-mm larva of Ambystomo as seen in dorsolateral view; B, 11 -mm Ambystomo,- 

 C' 23-mm Ambystomo,- D, 23-mm Sa/amondro in dorsol view with one half of the roof removed. (A, B, 

 C after DeBeer, 1937; D after Goodrich, 1930) 



otic process 



squamosal 



otic capsule 

 .columella (stapes) 



opercular muscle 



hyoid arch 



Figure 4-20. Otic capsule region of salamander (So/omondro) show- 

 ing operculum. (After Kingsbury and Reed, 1909) 



Description of the salamander would be incomplete with- 

 out reference to the operculum (Figures 4-19, 4-20). Whereas 

 the stapes is a part of the hyoid arch, the operculum 

 is a piece of the otic capsule wall, which becomes almost com- 

 pletely separated from that wall by a membranous gap. This 

 bit of wall never ossifies and serves for the insertion of an 

 opercular muscle that has its origin on the suprascapulum 

 of the pectoral girdle. This muscle (or ligament) functions 

 in transmitting sound vibrations from the pectoral girdle to 

 the inner ear. 



Frog or onuran The frog is a fine example of a highly 

 modified animal (Figure 4-21). The roof of the skull is much 

 reduced; the squamosal forms an incomplete temporal arch 

 and the fused frontal and parietal (frontoparietal) of either 

 side form the roof of the endocranium. There is no apparent 

 parietal foramen (see Figure 13-6). What is usually identi- 

 fied as the nasal is probably the prefrontal. Palatines are 

 present, and the pterygoid articulates with the otic capsule 

 behind the palatal division of the seventh cranial nerve. 



82 • HEAD SKELETON OF OTHER TETRAPODS AND CHOANATES 



