17] THE NASAL ORGAN IN AMPHIBIA— HIGGINS 17 



median rostrum is not present in any other Urodele, although prenasal 

 processes do exist in almost all types. Parker's homologies are hardly 

 borne out by our present knowledge. 



TRITON CRISTATUS 



The nasal capsule of Triton cristatus differs in several points from that 

 of either Amblystoma or Salamandra. In the younger of the two larvae 

 accessible (28 mm.), the chondrification of the capsule is far advanced and 

 I know nothing, except by inference, of the earlier stages. At this stage 

 (Fig. 16) the capsule is somewhat rectangular in outline, gradually tapering 

 toward the anterior end. The cristae trabeculorum {cr t) are well developed 

 and form with the trabeculae, the walls of the cavum cranii, pierced only 

 at their anterior margins by the large circular olfactory foramina (/o). 



Immediately in front of the crests, the trabeculae are united by a very 

 short planum basale {pb), which supports the olfactory lobes and the pos- 

 ior part of the intermaxillary glands; the latter, in this form, extending 

 backward beneath the anterior part of the brain. The planum basale in 

 Triton is very much smaller than that of Amblystoma, and lies more 

 posterior in respect to the other capsular parts. Dorsal to, and somewhat 

 anterior to the planum basale is a bar of cartilage which unites the capsules 

 of the two sides just in front of the olfactory foramina. This is the pons 

 ethmoidalis {pe), and is developed by medial growths from the dorsal part 

 of both capsule^ much as in Amblystoma to which it bears a resemblance. 

 Unlike Amblystoma, however, the pons is never united to the basale by 

 the planum verticale; but throughout life it is separated from it by a large 

 circular fenestra ethmoidalis (Jen eth) so that internasal space and cavum 

 cranii are separated from each other by membranous structures only. 



In contrast to the larval stages of most other Urodeles, the nasal organs 

 of Triton are almost entirely anterior to the forebrain, so that planum 

 basale and pons ethmoidalis are close to the posterior parts of the capsule. 

 As a result of the relation of the central nervous system to the nasal struc- 

 tures, each capsule appears as a segment of an elongate cone, obliquely 

 truncate anteriorly, with the anterior half of its lateral wall interrupted by 

 a very large narial opening. As is true for all Urodeles, the cartilage 

 structures of each side, in front of the planum basale, are separated by an 

 internasal space (the intermaxillary room of Born, 1877). which in Triton 

 is more elongate and extends between the walls of the anterior two-thirds 

 of the capsule. 



Anterior to its junction with the crista trabeculae, each planum tectale 

 ipt) curves outward and downward, completely covering the posterior 

 parts of the nasal sac and the choana; laterally it continues into the lamina 

 externa which covers the posterior part of the organ of Jacobson. More 

 posteriorly, each lamina externa has united to the anterior prolongation of 



