Skull of Tadpole. gr 



lets ; but in no animal does the cartilage, or bone, form an 

 integral part of the skull wall. It remains permanently in a 

 condition which is primitive and transitory in the case of the 

 auditory capsule. Finally, there is the capsule of, the olfactory 

 organ. This is also relatively unimportant, but does become an 

 actual, though a small, portion of the wall of the adult skull. 

 The upper nasal wall of the frog's skull appears to be partly or 

 entirely formed of the capsule. And in other vertebrates it 



Fig. 37.— Skull of Tadpole. Lateral view. ' (After Marshall.) 



The different elements which enter into the formation of the skull are indicated by 

 different shading. Cranium^ marked with vertical lines ; capsule of sense orga?i^ 

 dotted ; visceral arches, shaded with fine lines ; labial cartilages, marked with 

 horizontal lines, c.h, notochord ; e.c, auditoi-y capsule: Q. quadrate; Q.o, palato 

 pterygoid; q.r, articulation of quadrate ; H.R, ceratohyal ; H.Q, its articulation with 

 quadrate; H.o, urohyal; R.L, trabecuke cranii ; L.L, L.u, labials; M.c, Meckel's 

 cartilage ; JU, JL, jaws ; li, lj, lips ; bs, cerebi-al hemisphere ; I'N, lineal body. 



enters into the formation of the cartilages which protect the nasal 

 organ. 



3. In the tadpole, which breathes by means of gills, the side 

 of the throat is pierced by four gill-clefts, which are slits putting 

 into communication the interior of the pharynx with the exterior. 

 The walls of these gill-clefts (for a further description of which 

 see p. 135) are strengthened by the appearance oi cartilaginous 

 bars. Of these, the first and part of the second form an integral 

 part of the adult skull. The first arch is termed the mandibular; 

 it sends forward a process which becomes fused with the skull 



