Henry L. Bruner 91 
bularis Hoffmann) whose anterior portion lies directly above the pos- 
terior extension of the sinus orbitalis. All of these movements, however, 
would tend to produce uniform elevation of blood-pressure throughout 
the head. In the snake there is no means of closing the outlets of the 
sinus orbitalis and creating local high pressure in the anterior head 
region. 
The reduction of the flooded sinus orbitalis of the snake is effected 
chiefly by the muscles of the bulbus, but the process is facilitated by the 
general elasticity of the tissues. Owing to the absence of movable eye- 
lids, the m. depressor palpebre inferioris is wanting, as is also the 
smooth muscle of the orbit (m. compressor sinus orbitalis). 
Fig. 15. Hydrophis hardwickii. The external nasal openings are closed 
by spongy tissue, chiefly by a swelling of the rostral wall of the nasal 
vestibule. 
The flooding of the sinus vestibuli nasi produces effects which are 
easily observed in the sea snakes, where the external nasal opening may 
be closed by the spongy tissue of the nasal vestibule (Text Fig. 15 and 
Fig. 4, Plate IL). Shght movements of a similar nature occur also in 
Colubroidea, but the spongy tissue is sparingly developed and the nasal 
opening cannot be closed in this group. 
C. SIGNIFICANCE OF THE SWELL MECHANISM OF THE 
OPHIDIAN HEAD. 
Concerning the ultimate significance of the swell mechanism of the 
Ophidian head there is little room for doubt, for the snakes have the 
same moulting habits as the lizards and there is apparently the same need 
of a moulting mechanism. In view of this fact and because of the close 
