%2 The Cephalic Veins and Sinuses of Reptiles 
the neck. Similar subcutaneous spaces exist in the supraoccipital 
region. 
The high blood-pressure which distends the capillaries, veins, and 
sinuses of the head, produces at the same time extensive movements of 
the lymph. Such a movement is well illustrated in the case of the lymph- 
sinuses of the orbit and eyelids. Owing to the distension of the sinus 
orbitalis the lymph is forced out of the deeper sinuses of the orbit; the 
large supraciliary and inferior orbital sinuses are emptied and a large 
part of the escaping fluid enters the sinuses of the eyelids, thus pro- 
ducing the characteristic swelling of the hds which accompanies the dis- 
tension of the sinus orbitalis. Similar movements on a smaller scale 
probably occur in all of the soft parts of the head, the distension of the 
deeper blood-vessels causing a flow of lymph toward the subcutaneous 
sinuses, while at the same time the movement of the lymph toward the 
trunk region is accelerated. Both of these movements are probably aug- 
mented in another way. Under high blood-pressure the rate of transu- 
dation from the blood-vessels is probably accelerated and the total amount 
of the lymph in the tissues is increased. 
After the reduction of the distended veins and sinuses and the resto- 
ration of normal blood-pressure, the lymph-pressure also falls and the 
lymph finds its way back to the deeper sinuses and spaces. The lymph- 
sinuses of the eyelids are emptied by their smooth musculature, the lymph 
returning, for the most part, into the supraciliary and inferior orbital 
sinuses, which, as already stated, le external to the m. compressor sinus 
orbitalis. The orbital lymph-sinuses thus provide in a most convenient 
way for the prompt flooding of the sinuses of the eyelids, the distension 
of the latter following automatically, as it were, whenever the sinus 
orbitalis is flooded. 
f. Summary oF EVENTS wHicH Occur DURING THE OPERATION OF 
THE SWELL MECHANISM. 
The chief events which occur during the operation of the swell 
mechanism in Anolis may now be briefly summarized as follows: 
I. First stage of intumescence. 
1. Contraction of the m. constrictor ven jugularis interne; relaxa- 
tion of the orbital muscles. The constrictor muscle obstructs the chief 
efferent blood-vessel of the head and causes distension of veins, sinuses, 
and capillaries. Asa result of this the lymph flows toward the superficial 
spaces, while at the same time the rate of transudation is probably 
increased. 
2. The rise of blood-pressure is followed by acceleration of the beat 
