49] THE NASAL ORGAN IN AMPHIBIA—HIGGINS 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 
