a) 
Henry L. Bruner 63 
tion of the m. temporalis during the second stage of orbital protrusion 
is easily seen in Anolis and the effect is not open to doubt. The muscle 
supports the fascia which forms the posterior wall of the sinus orbitalis. 
When the muscle is relaxed during the first stage of orbital protrusion, 
the blood-pressure in the sinus orbitalis pushes the muscle backward. In 
the second stage of protrusion the muscle contracts, its anterior portion 
presses against the flooded sinus orbitalis; the blood-pressure is raised 
and the protrusion of the eye is increased. 
(4) The Bucco-pharyngeal Muscles—No attempt has been made to 
analyze the movement caused by these muscles and its significance is not 
entirely clear. It is essentially a swallowing movement, and includes 
elevation of the floor of the mouth and contraction of the pharyngeal 
muscles. By elevating the floor of the mouth it is possible that pres- 
sure may be applied against the floor of the orbit, where the large sub- 
orbital foramen is closed only by soft tissues. Suitable pressure in this 
region by means of the tongue or hyoid apparatus would augment the 
protrusion of the eye, as may be easily demonstrated by artificial means. 
Efforts to observe such movements of the hyoid apparatus, however, were 
unsuccessful, for the attempt to hold the mouth open led in all cases 
to a suspension of the movements. 
The contraction of the pharyngeal muscles probably assists in pro- 
ducing higher blood-pressure in the posterior part of the head. Such 
a result would probably follow from the pressure of the contracting 
muscles upon the flooded veins and sinuses. 
In accordance with the above account, I conclude: 
The protrusion of the eye of the lizard is caused by the distension of 
the sinus orbitalis and the elevation of blood-pressure in the same. 
In the first stage of protrusion the observed effects are due, in a large 
measure, to the contraction of the m. constrictor vene jugularis interne. 
As a result of such contraction, blood accumulates in the sinus orbitalis 
and the blood-pressure rises until it reaches a maximum for the existing 
arterial pressure. This condition is ordinarily attained in Anolis in 
about five seconds, but the time required is subject to some variation. 
In the second stage, or stage of high pressure, the m. constrictor venze 
jugularis interne maintains its tonus; the outlet of the sinus orbitalis 
is closed by the m. protrusor ocul, which at the same time pushes against 
the membraneous wall of the sinus and raises the blood-pressure to a 
higher level. As a result of this the orbital protrusion is increased by 
stretching the elastic lateral wall of the sinus. 
