49] THE NASAL ORGAN IN AMPHIBIABIGGINS 49 



THE NASAL CAPSULES OF THE ANURA 



PIPA AMERICANA 



The Surinam toad, a representative of the aglossate Anura, is unique 

 among the Amphibia in its quiescent larval period, during which, the entire 

 development takes place; so that the adult characters are formed before 

 the animal takes up its free existence. 



Parker (1876) has described the chondrocranium of a Pipa larva, 

 considerably younger than my single stage, in which the complete fusion of 

 the trabecular plates has obliterated the large hypophysial fenestra, so 

 common to most amphibian skulls. In Parker's larva, the coalesced 

 trabeculae form a broad, slightly emarginate internasal plate, which 

 extends forward to the tip of the skull, where from each lateral margin a 

 slender process bends posteriorly and, passing beneath the nasal organ, 

 terminates in a rounded projection near the middle line of the capsule. 

 Parker calls these processes the 'recurrent trabeculae', but it is easy to see 

 that they are modified cornua, which in Pipa are more cylindrical than in 

 most Urodeles, more like those in Cryptobranchus. 



In my single stage, a Pipa larva two-thirds of an inch long, much of the 

 cartilage of Parker's stage has been resorbed and the' chondrocranium is 

 more like that of other Amphibia. The broad intertrabecular floor is now 

 reduced to a pair of trabeculae, which, with greatly reduced cristae, reach 

 forward to the level of the eye, where they are united by a planum basale 

 as in UrOdeles (Figs. 34, 35, pb). This planum basale is broadly concave 

 dorsally (Fig. 73, pb}, and supports the olfactory lobes which lie above the 

 posterior parts of the nasal organ; so that the olfactory nerve, which leaves 

 the olfactory lobe from its ventral margin, passes through a large median 

 foramen olfactorius (fo) in the basale, reaching the nasal sac at the choana. 

 More anteriorly the planum basale narrows considerably, covering only 

 the medial parts of the nasal sac and the nasal glands; at the same time 

 expanding ventrally into a prominent keel, which separates the choanae 

 of the two sides. Farther forward the planum basale is continuous with 

 the planum verticale, which reaches forward to the tip of the skull, there to 

 unite with other parts yet to be described thus completely separating the 

 nasal organs of the two sides. 



From each lateral angle of the planum basale, a small planum tectale 

 (pt) passes obliquely outwards and forwards, covering the posterior part 

 of Jacobson's organ where it empties into the nasal sac. At its lateral 



