11] THE NASAL ORGAN IN AMPHIBIA—HIGGINS 11 
and the posterior lateral angle nearly meets the lateral margin of the tec- 
tale (Fig. 5). Medially and behind, the cornu is continuous with the 
planum basale, which has now extended laterally so as to form a partial 
floor beneath the medial side of the olfactory sac. In all Urodeles the 
produced postero-lateral angle of the cornu supports the organ of Jacobson 
(vomeronasalis). This relation and also that of the organ to the lateral 
part of the tectale is of great aid in determining the homologies of the more 
complex capsule of the adult. 
The antorbital process (pa) is now larger, forming a plate rather than a 
bar, and its antero-lateral angle is directed forward as a blunt process which 
nearly meets the posterior process of the cornu and also the lateral margin 
of the tectale. 
In the nasal capsule of a 45 mm. larva, only a few modifications need 
description. The capsule (Figs. 7, 8) has not increased in length, although 
there has been an appreciable increase in width and depth. With the 
greater development of the olfactory lobes there has been a corresponding 
increase in the size of the cavum cranii (cc). The olfactory lobes extend 
forward only as far as the caudal third of the nasal sac, so that the olfactory 
foramina look obliquely forward from the antero-lateral angles of the brain 
case. There is a gradual change during growth in the relative positions of 
the nasal sac and the forebrain. In the earlier larva, brain and olfactory 
organs overlap for about half the length of the nasal sac, while in the adult 
the sensory structures are almost entirely in advance of the tip of the 
olfactory lobes, approximating the anuran condition. 
The planum verticale (fv) of this stage is shorter than before but its 
height is almost twice that of the 34 mm. larva; so that this stage marks the 
beginning of the reduction of the verticale which is so much smaller in the 
last stage to be described. 
The only other features to note in this stage are the broadening of the 
tectale, which process has brought the foramen for a branch of the nasalis 
internus on to the dorsal surface of the capsule and the extension of the 
antero-lateral angle of the tectale, so that it now fuses with the postero- 
lateral angle of the cornu, forming the first appearance of a lateral wall to 
the capsule. The naso-lacrimal duct passes over this connection between 
cornu and tectale, and empties into the olfactory sac just above the 
anterior end of Jacobson’s organ. 
Procartilage cells are abundantly distributed over the anterior end of 
each olfactory sac, the anterior naris being terminal in all larval stages. 
From these cells, the anterior cupola is formed; a process which involves 
the shifting of the naris to its lateral position. 
In a larva near the end of metamorphosis (Fig. 9) many changes of the 
capsule of the early stage have occurred. The general proportions of the 
capsule remain unchanged, although there has been a further reduction in 
