198 AYERS AND JACKSON. [Vol. XVII. 



The nasal tube (Plate XXII, Figs. 5, 6, NT) is a direct 

 anterior continuation of the olfactory capsule. It is slightly- 

 funnel-shaped, being widest at the anterior end, and narrowest 

 a short distance in front of the posterior end. The length of 

 the nasal tube is greater than that of the olfactory capsule 

 and cranium combined. The nasal tube and the olfactory cap- 

 sule have a combined length about twice that of the cranium. 

 Anteriorly the nasal tube opens to the exterior. Posteriorly 

 it communicates with the olfactory capsule and the hypo- 

 physial tube, as previously described. The membranous wall 

 of the tube is supported dorsally and laterally (and to some 

 extent ventrally) by a series of cartilaginous nasal arches. 

 When viewed from the sides, or from above, these arches 

 appear as rings ; but when viewed from below, it is seen that 

 the ventral fourth of the ring is lacking. The nasal arches are 

 usually nine in number, but sometimes eight or ten. The an- 

 terior four, and the posterior two arches have cartilaginous con- 

 necting processes ; the remaining arches are independent. The 

 anterior arch is the largest and widest. It is inclined sharply 

 forward, its plane making with the horizontal plane an angle of 

 about 45°. The anterior, or first arch is connected with the 

 second by a median dorsal connecting process. Inferiorly, the 

 first four arches end on each side in a longitudinal connecting 

 bar. This bar ends in two terminal processes. The anterior 

 process extends downward, inward, and forward, curving around 

 and running forward parallel to the corresponding process from 

 the opposite side. The two processes end near each other in 

 the anterior inferior margin of the nasal tube, but do not con- 

 nect, either with the labial cartilages or with each other. (In 

 one case the two processes were found fused together, so 

 that a complete cartilaginous ring was formed surrounding 

 the anterior end of the nasal tube.) The posterior terminal 

 processes of the connecting bar arise opposite the ends of the 

 third and fourth arches. They are short, extending downward, 

 inward and forward, ending in a free tip. The posterior two 

 nasal arches are either fused together in the median dorsal 

 line, or connected by a short process. Their ends are not 

 connected. The last nasal arch connects with the cartilages 



