. Chordate morphology. Morphology (Animals); Chordata. 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 caps
. Chordate morphology. Morphology (Animals); Chordata. 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. Please note that these images are extracted from scanned page images that may have been digitall
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