50 THE SKELETON OF THE FROG. 
Fig. 8. The frog’s skull, from the ventral surface. 
a, parasphenoid: c, columella: e, exoccipital: f.p, frontoparietal: m, 
maxilla: 2, vomer: 0, pro-otic: p, pterygoid: pa, palatine : pm, premaxilla : 
q, quadratojugal: se, sphenethmoid. 
2. The sense capsules: cartilaginous and bony capsules 
which surround and protect the olfactory and auditory 
organs; and are fused with the cranium proper so 
as to form parts of the skull. 
a. The auditory capsules are fused with the sides of the 
posterior end of the cranium, to which they form 
wing-like projections: they consist largely of cartilage. 
a. Cartilage Bones of auditory capsules. 
i, The pro-otics: a pair of irregular shaped bones in 
the anterior walls of the capsules, and forming 
also parts of their roof and floor. 
b. The olfactory capsules are fused with the anterior end 
of the cranium, and also with one another. They 
consist very largely of cartilage, which is produced in 
front into the rhinal processes. 
a Cartilage bones of olfactory capsules. The spheneth- 
moid as already noticed extends forwards so as to 
invade the olfactory region, but does not properly 
belong to the olfactory capsules. 
