Henry L. Bruner 109 
m. constrictor vene jugularis interne, which obstructs the chief efferent 
vessel of the head (vena jugularis interna). This muscle is located in 
the parotic region (lizard and turtle) or in the anterior cervical region 
(snake), at a point which controls the entrance of the more posterior 
cephalic tributaries of the vein, where the vein, under ordinary condi- 
tions, transmits nine-tenths of all the blood from the cranium, face, and 
jaws. 
The constrictor muscle is innervated by fibers which come from the 
ganglion superius vagi (lizard and turtle) or from the ganglion trunci 
vagi (snake). In view of its innervation and general relations, the 
muscle has probably been derived from a branchial muscle of amphibian 
ancestors. 
3. In the Sauria the swell mechanism includes also a m. protrusor 
oculi, the m. temporalis, and the bucco-pharyngeal muscles. The m. pro- 
trusor oculi is a hitherto undescribed muscle which hes at the origin of 
the vena jugularis interna from the sinus orbitalis. In contraction it 
obstructs the vein and at the same time presses against the membraneous 
wall of the smus. In some lizards a second protrusor muscle occurs, 
m. protrusor oculi accessorius, which hes directly behind the orbit, 
lateral to the m. protrusor ocul. 
The protrusor muscles derive their nerve supply from the ramus 
mandibularis V. 
4, The above-mentioned muscles usually contract in a certain sequence 
and produce two distinct stages of intumescence: a first stage with an 
average duration of about five seconds, and a second stage with a dura- 
tion of about one-half second. The second stage is immediately followed 
by a stage of reduction. These three stages form a normal cycle of 
intumescence. 
5. The first stage of intumescence begins with the contraction of the 
m. constrictor vene jugularis interne. The accumulation of blood is 
facilitated by relaxation of the orbital muscles and acceleration of the 
heart-beat, probably, also, by vaso-motor adjustments, including both 
dilation of the cephalic arteries and constriction of those leading to the 
posterior parts. During this stage all veins and sinuses of the head are 
rapidly filled and distended, the orbital region is protruded and more or 
less swelling occurs in other parts of the head. 
6. The second stage of intumescence is marked by the contraction of 
the m. protrusor oculi, m. temporalis, and the bucco-pharyngeal muscles. 
the m. constrictor vene jugularis interne also maintaining its tonus. 
The result is a sudden increase of blood-pressure in the sinus orbitalis, 
the orbital region is more strongly protruded, and a wave of high blood- 
