8 
sutural surface for union with the prefrontal and lachrymal. Superiorly 
the outer and inner walls of the nasal unite and extend upward, as a very 
thin sheet of bone, to flank the posterior process of the upper limb of the 
premaxilla and form the outer portion of the postero-superior part of the 
hood. 
The inner view (Plate I, figure 1, N.) presents a smooth, flat surface 
except for a rather large excavation in the anterior portion. This repre- 
sents the posterior boundary of the narial passage as it turns sharply down- 
ward and forward to the internal naris. The flat, inner wall meets that 
of the opposite nasal and near its centre it is pierced by a large semi-reni- 
form fenestra which allows communication between the large cavities within 
the nasals. 
Narial Passage and Air Reservoir . The external naris appears to have 
been situated near the front of the premaxilla, and the narial passage 
throughout most of its length was within this much modified bone. In 
its anterior portion it is enclosed supero-externally by the upturned 
external edge of the bone. In this region the passage is fairly large, but 
just behind where the premaxilla divides into upper and lower limbs it 
narrows somewhat and then enters an enlarged cavity in the lower limb. 
From this cavity the passage turns sharply forward and enters a large 
chamber in the upper limb, runs backward in the upper limb to where it 
meets the nasal and then takes a sharp turn downward and forward to the 
internal naris. In their downward course the narial passages unite and 
are surrounded by the forwardly developed processes of the nasals. (In 
Lambeosaurus the greater development of the upper limbs of the pre- 
maxillae seem to make the division of the narial passages complete.) Y/hat 
Parks referred to as the deep vault, on the under side of the crest of 
C , intermedins (14, page 15, Figure 1), represents the united narial pas- 
sages, In the disarticulated hood (Plate I, figure 1, Nar. P.) this down- 
ward extension of the narial passage appears to lie in a deep trough in the 
nasal, but when the nasals are articulated it is subcylindrical in form and 
enclosed by these bones. The prevomers divide the narial passages at the 
internal nares. The internal naris is separated from the narial passage in 
the lower limb of the premaxilla by only a thin wall, yet the air must 
have come through a passage more than 500 mm, long, including S- and 
U-shaped traps, to reach this point. 
The internal naris is bounded anteriorly and externally by the pre- 
maxilla and maxilla, posteriorly by the palatine and upturned edge of the 
pterygoid, and internally by the prevomer. 
Within the swollen nasal bone is a large pocket which extends to the 
postero-inferior angle of the bone. This pocket is carried forward into the 
side of the hood and is flanked by the lower limb of the premaxilla, thus 
forming a large subsidiary air reservoir. There was free communication 
between this reservoir and the narial passage above where the nasals com- 
pletely surround the united narial passages. There was communication 
between the right and left air reservoirs through large, semi-reniform 
fenestrae through the inner walls of the nasals and between the narial pas- 
sages, by fairly large fenestrse through the inner walls of the upper limbs 
of the premaxillae, just in advance of their contact with the nasals. In 
