PAPERS ON BIOLOGY AND AGRICULTURE 133 



strikingly U-shaped in section (Figs. 7, 8), the other limb 

 being entirely free from the inner except at the anterior 

 margin where both limbs are joined dorsally by a small 

 bar of cartilage. This small cartilage is absent from the 

 skull of Rana, where the limbs of this muscularis process 

 are entirely free from each other except ventrally, where 

 even as in this stage of Bufo they are joined to continue 

 forward to a prominent pterygoid process. The anterior 

 margin of tl;e inner limb of the musculars process bears a 

 prominent round structure which, although lacking any 

 reference to the nasal organ as such, is known as the 

 quadrato-ethmoidalis process, and corresponds with a 

 similar region in the frog (QEP, Fig. 6). 



Continuing forward from the anterior ventral surface 

 of the muscularis of the quadrate is a broad band of car- 

 tilage, the pterygoid process (PP, Fig. 6). Each ptery- 

 goid continues forward to the position of the mouth and 

 joins its mate at a point considerably posterior to the 

 pons trabeculae, above described, and in a maimer similar 

 to it, thus forming the pons pterygoidii (PPT, Figs. 2, 3). 

 In its posterior part each pterygoid is conspicuously 

 broad; approximately flat on its upper surface, but pos- 

 sessed of a conspicuous keel on its lower. Just anterior 

 to this broad portion each pterygoid bends abruptly 

 toward the median line and expands into a prominent 

 vertical platp which extends dorsally to a point just be- 

 low the vertical margin of the trabecula. This portion 

 of the pterygoid (Figs. 3, (>) is conspicuously concave on 

 its external surface, and lies just within the expanded 

 cornu trabeculae, the inner surface of which is markedly 

 convex, so that there comes to be formed a conspicuous 

 oval fenestra between these portions of the capsule. 

 Thus it is evident that the anterior portion of the capsule, 

 consisting of trabeculae, pons and cornua, form a hood- 

 like structure which fits over the anterior portions of the 

 pterygoids and the pons, uniting them (Fig. 3). 



As we contrast this nasal capsule, just described, with 

 that of the older toad at the time of metamorphosis, it is 

 quite easy to recognize the changes that have taken place 

 in the transformation. These changes concern only those 

 portions definitely related to the nasal organ, and thus 



