60 The Cephalic Veins and Sinuses of Reptiles 
a. DISTENSION OF THE SINUS ORBITALIS AND PROTRUSION OF THE EYES. 
As already stated in the preliminary description given above, the pro- 
trusion of the eye of Anolis includes two distinct stages: 
In the first stage, or stage of distension, the sinus orbitalis gradu- 
ally fills with blood and the bulbus is moderately protruded. No muscle 
movements are visible in the region of the eye or elsewhere, and the 
intumescence 1s apparently due wholly to blood-pressure. As a result of 
this pressure the eyelids are usually closed, chiefly by the elevation of 
the lower lid, while both lids become turgid with blood and lymph, the 
latter being forced, by the great blood-pressure, from the deeper sinuses 
and channels into the lymph-spaces of the lids. 
The average duration of this stage is five seconds, but it may be either 
longer or shorter, the greatest length observed being about fifty seconds. 
With the average duration of this stage a maximum enlargement is at- 
tained which amounts to about three-fifths of the final maximum which 
occurs at the close of the second stage. With less than the average 
duration the amount of enlargement is less, while prolongation beyond 
the average results simply in the maintenance of a uniform state, which 
represents, therefore, the maximum effect possible under the prevailing 
conditions. 
The second stage of orbital enlargement is a stage of high blood- 
pressure. It is characterized by a sudden protrusion of the eyes, ener- 
getic contraction of the muscles of mastication, and elevation of the floor 
of the mouth. The eyelids remain closed and the membrana nictitans is 
more or less protracted, presumably as a result of the great blood- 
pressure. The duration of this stage in Anolis is usually about one-half 
second. 
1. ACTIVITY OF MUSCLES. 
1. FIRST sTaGE.—The flooding and distension of the sinus orbitalis 
during the first stage is due to a combination of several different causes. 
One of the most important of these is the m. constrictor vene jugularis 
interne. The contraction of this muscle during the first stage of orbital 
protrusion is shown by the following facts: 
(1) The amount of protrusion and the rate of enlargement both indi- ~ 
cate the obstruction of the vena jugularis interne, the outlet of the sinus 
orbitalis. The flooding of this sinus is not simply a vaso-motor effect. 
(2) The general intumescence which accompanies the protrusion of 
the orbital region locates the obstruction in the posterior cephalic region. 
Outside of the orbital region more or less evident swelling occurs in 
