Henry L. Bruner 61 
other parts of the head, from the nasal openings to the occiput. Especi- 
ally significant, however, is the intumescence which occurs in the region 
of the external auditory depression, where the vena mandibularis and 
its tributaries lie close to the skin. The intumescence in this region is 
especially marked in those forms which are provided with a thin skin 
and small scales. In Anolis, for example, the swelling is accompanied 
by a considerable separation of the scales, while the thin integument be- 
tween the scales is intensely reddened by the increase of blood in the 
subjacent veins. These phenomena are undoubtedly due to unusual 
turgescence of the vena mandibularis,—a vein which penetrates the con- 
strictor muscle to enter the vena jugularis interna. These facts clearly 
point to the obstruction of the vena jugularis interna by the constrictor 
muscle. 
Jxperimental evidence leads to the same conclusion. The artificial 
obstruction of both vene jugulares interne produces results which re- 
semble in all respects, excepting perhaps in degree, the natural flooding 
of the sinus orbitalis and other cephalic veins during the first stage. 
We may safely conclude, therefore, that the flooding and distension of 
the sinus orbitalis during the first stage is caused, in part at least, by 
the contraction of the m. constrictor vene jugularis interne. As a re- 
sult of this contraction the jugular vein is blocked, the blood accumulates 
in the peripheral part of the vein and the escape of blood from the sinus 
orbitalis is prevented. The sinus itself is then distended, partly by blood 
which is poured into it by its numerous tributaries, partly by blood which 
comes directly from the capillaries. The amount of the distension is 
determined by the arterial blood-pressure, which keeps the blood flowing 
into the sinus until the venous pressure almost equals that of the local 
arteries themselves. At this point distension of the sinus ceases and the 
protrusion of the orbital region also reaches a maximum, in so far as it 
may be affected by the circulatory mechanism. Then follows the second 
stage. 
2. SECOND STAGE.—During this stage the constrictor muscle maintains 
its tonus, as indicated by the persistence of the postorbital swelling. On 
account of the great number of muscles employed, the study of this 
stage presents a somewhat difficult problem. It is believed, however, 
that the following description contains all of the important factors, with 
the approximate function of each: 
(1) Musculus Protrusor Ocult (m. p. o., Figs. 4 and 5, Plate I, Figs. 1 
and 2, Plate III, and Fig. 1, Plate I1).—The immediate function of this 
muscle has been already stated. Its contraction during the second stage 
