THE FROG 39 
preparation), on which are deposited the following membrane 
bones: 
The angulo-splenial, a long bone forming the posterior part of 
the arch; posteriorly it articulates with the maxillary arch. It 
is grooved on the upper and outer surface for the reception of 
Meckel’s cartilage. 
The dentary, a thin flat bone lying on the outer surface of the 
anterior half of Meckel’s cartilage. 
The mandibular arch is completed in front by two small carti- 
lage bones, the mento-meckelian bones; these are ossifications in 
Meckel’s cartilage, on each side of the median line. They are 
opposed to the premaxillz, and as previously explained form part 
of the mechanism for closing the nares. 
Compare the mandibular arch of the frog with that of an 
elasmobranch (e. g., a skate or a dogfish). 
(c) The hyoid apparatus. The main body of the hyoid con- ° 
sists of a cartilaginous plate lying in the floor of the mouth. The 
following are its more important processes: (1) the anterior 
cornua, slender cartilaginous rods, one on each side, extending 
backward and upward to their points of attachment to the lower 
side of the auditory capsules; (2) the posterior cornua or thyro- 
hyoid processes, which are a pair of stout bony processes diverg- 
ing from the posterior border of the body of the hyoid; and 
(3) the lateral processes, short cartilaginous projections just in 
front of the thyrohyoid processes. 
Compare the hyoid apparatus of the frog with the more fully 
developed hyoid and branchial apparatus of an elasmobranch 
(e. g., a skate or a dogfish). The anterior cornua of the frog 
correspond to the hyoid arch of the elasmobranch, the lateral 
and posterior processes are vestiges of branchial arches, while the 
body of the hyoid represents the fused ventral ends of the hyoid 
and branchial arches. In the tadpole stage of the frog and the 
toad, branchial arches are present much as in the adult elasmo- 
branch (see Leuckart’s chart). 
B. The Appendicular Skeleton.—This consists of the bones of 
the limbs, and the girdles (pectoral and pelvic) which unite them 
to the axial skeleton. With the exception of the clavicles, all the 
bones are cartilage bones. 
