132 ILLINOIS STATE ACADEMY OF SCIENCE 



capsule, relatively small at this stage, forms in the later 

 larva the entire floor, and supports the nasal organs as 

 well as the nasal glands found within the cavity. 



At the anterior end of the nasal organ the planum eth- 

 moidalis bifurcates, forming the cylindrically flattened 

 trabeculae (T, Figs. 1, 6), which diverge forward, point- 

 ing ventrally in the mouth region. The trabeculae, al- 

 though separated throughout their entire length by a 

 triangular internasal space, are joined distally by a car- 

 tilaginous plate, the pons trabeculae (PT, Fig. 1). At 

 the region of the junction of the pons, each trabecula 

 curves ventrally for a short distance, and then by a broad 

 curve forms a prominent corna trabeculae (CT, Fig. 6), 

 which ends in a small posteriorly directed process closely 

 applied to the pterygoid cartilage of the upper jaw. Con- 

 trary to the usual position of the cornu trabeculae of the 

 Urodeles, each comu of the toad is directed ventrally 

 and posteriorly instead of laterally, although the general 

 shape of these structures is quite identical in these 

 groups. A further contrast is to be noted in the relation 

 of the nasal organs to the cornua. In the Urodeles the 

 external naris is terminal and the anterior portion of the 

 nasal organ lies directly upon the cornu trabeculae which 

 thus supports it. In the toad, on the other hand, the 

 narial aperture is more dorsal and considerably back 

 from these anterior parts of the capsule, so that here 

 there is no intimate association between the nasal sac 

 and the cornu. Later, however, it is probably true that 

 as development ensues, each cornu forms an integral 

 part of the capsule, and as the nasal organ assumes 

 greater proportions comes to rest upon it. 



Although not definitely a part of the nasal capsule, 

 yet rather intimately connected with it in the earlier 

 larval stages is a prominent curved plate of cartilage 

 connected with the anterior margin of the planum basale 

 at its junction with the alisphenoid cartilage. This is the 

 muscularis process of the quadrate (MPQ, Figs. 1, 6) 

 which in the earlier stages is attached to the anterior 

 portion of the chondrocranium, but later migrates pos- 

 teriorly and at metamorphosis takes its position in rela- 

 tion to the suspension of the jaws. This structure is 



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