Henry L. Bruner 69 
the orbital muscles maintain a proper tonus, such distension may occur 
without enlargement of the sinus orbitalis. 
The provision for local control of the sinus vestibuli nasi is evidently 
of considerable importance. It affords, on the one hand, the possibility 
that the external nasal openings may be constricted or closed without 
interfering with other functions of the head. On the other hand it 
permits a general distension of the cephalic veins and sinuses without 
disturbing the olfactory and respiratory organs. 
More or less pronounced movements, due to the distension of the sinus 
vestibuli nasi, are of common occurrence among the lizards. In Lacerta 
the spongy tissue is unequally developed around the margin of the ex- 
Fie. 8. Rostrum and nasal openings of Phrynosoma cornutum. 
The openings are almost closed by spongy tissue, which forms a prominent 
cushion, n, at the posterior margin of each opening. 
ternal naris and the visible movements are limited chiefly to the pos- 
terior and ventral parts of the opening. Complete closing of the 
external opening does not occur, but conditions are favorable for the 
closing of the deeper part of the nasal vestibule, where the spongy tissue 
is better developed. In Phrynosoma the spongy tissue completely sur- 
rounds the external naris, but it is much thicker about the posterior 
margin of the opening (n., Text Fig. 8). When the sinus vestibuli nasi 
is distended this part of the spongy tissue (st., Fig. 5, Plate II) swells 
up, cushion-like, and closes the opening. This function of the spongy 
