(op) 
o 
Henry L. Bruner 
after the second stage of intumescence. During the first stage the cardio- 
accelerator center evidently gets the upper hand. 
(2) Vaso-motor Adjustment of Arteries—In view of the increased 
activity of the heart during the distension of the veins and sinuses, it is 
probably safe to assume the vaso-dilation of the carotids and their cephalic 
branches. Indeed, a mechanical distension of these arteries would natur- 
ally follow from higher blood-pressure alone, unless it were prevented 
by constriction of the vessels. 
I have not been able to discover a direct opening of arteries into the 
sinus orbitalis. The arteries which feed the sinus break up into capil- 
laries, which run a short distance through the tissues and then widen out , 
gradually to open into the sinus. Hven under such conditions, however, 
the dilation of the arteries leading to the sinus would hasten a process 
which, at best, involves more or less disturbance of the normal functions 
of the eye. 
The accumulation of an extraordinary amount of blood in the head 
probably requires, also, constriction of the posterior arteries of the body. 
During the distension of the cephalic veins and sinuses of Anolis, the 
quantity of blood in the head is probably doubled. The extra amount, 
which is equal to one-sixth of the total amount in the body, must be 
withdrawn from the posterior parts. ‘This would seem to require exten- 
sive vaso-motor changes, including both dilation of the arteries leading 
to the head and constriction of the posterior arteries. 
(3) Striated Muscles of the Orbit—Under ordinary conditions a 
slight dilation of the sinus orbitalis follows the relaxation of certain 
striated muscles of the orbit, especially the m. retractor oculi and the 
m. depressor palpebre inferioris (m. adductor maxille inferioris, Fischer, 
52). ‘This fact is easily demonstrated by the use of curare. About one 
drop of a 1 per cent solution injected hypodermically in the dorsal trunk 
region is followed by a perceptible protrusion of the eye in about five 
minutes. In twenty minutes the control of the voluntary muscles is lost, 
the lower eyelid rises, the bulbus protrudes, and the orbital enlargement 
is quite marked. 
This experiment shows: 
(a) That ordinary blood-pressure in the sinus orbitalis is sufficient to 
produce a certain amount of distension of the sinus. Such pressure, in- 
deed, is the most important factor in the closing of the eye, which is 
due chiefly to the elevation of the lower eyelid. Under ordinary condi- 
tions the m. depressor palpebre inferioris maintains a certain tonus 
sufficient to force the blood out of the palpebral part of the sinus orbit- 
5 
