| fontanelle largest in | about uniform width | parietal region. | throughout length of | | fontanelle. | | Nasals | Moderate in size; | Long and broad; | slightly wider | arcuate in dorsal | anteriorly than | view. | posteriorly in dorsal | | view. | | | Sphenethmoid | Moderately short in | Moderately short in | dorsal view. | dorsal view; ossified | | anteriorly between | | nasals. | | Columella | Distal and not | Distal and not | expanded. | expanded. ---------------+------------------------+------------------------ [Illustration: Fig. 5. Dorsal views of the skulls of (a) _Hyla m. microcephala_ (KU 68293) and (b) _H. sartori_ (UMMZ S-2677). Both × 12.] [Illustration: Fig. 6. Dorsal views of skulls of (a) _Hyla phlebodes_ (KU 68303) and (b) _H. robertmertensi_ (KU 59917). Both × 12.] Despite the great reduction in the ossification of the cranial elements, certain apparently consistent differences exist between the species seem to be consistent. The most notable differences are: 1) amount of ossification of the frontoparietals and consequent shape and size of the frontoparietal fontanelle, 2) shape of the nasals, 3) shape and extent of the sphenethmoid, and 4) shape of the columella (Table 4, Figs. 5-6). On the basis of these characters, _Hyla microcephala_ can be set apart from the other species and characterized as having a poorly ossified frontoparietal and correspondingly large frontoparietal fontanelle; long, slender, arcuate nasals; extremely short sphenethmoid; and expanded distal end of the columella. The other species in the group (_phlebodes_, _robertmertensi_, and _sartori_) have more ossification of the frontoparietals, broader nasals, only a moderately short sphenethmoid, and an unexpanded distal end of the columella. Among these three species, the skulls of _phlebodes_ and _robertmertensi_ are most nearly alike, whereas the skull of _sartori_ differs by having a differently shaped frontoparietal fontanelle, broader nasals, and an ossified anterior extension of the sphenethmoid between the nasals (compare Fig. 5b with Fig. 6 a-b).