Henry L. Bruner fal 
muscles, which probably compress the veins of the posterior part of the 
head, and thus, by raising the blood-pressure, tend to neutralize the effects 
of the contraction of the m. protrusor ocul. 
The significance of the large palatine sinuses is not entirely clear. On 
account of their numerous anastomoses they serve to equalize the blood- 
pressure in different parts of the head. Under ordinary conditions they 
may be used as reservoirs for the storage of blood, which, after obstruc- 
tion of the vena jugularis interna, is forced out to assist in the distension 
of the more dorsal vessels. On the other hand, however, it may be neces- 
sary to consider the palatine sinuses as mere incidents of a process which 
has for its object the protrusion of the eye and distension of other veins 
and sinuses of the head. 
The function of the sinus dentalis is also quite obscure. After ob- 
struction of the vena jugularis interna it possibly serves as a reservoir 
for the overflow of blood from the mandibular veins. 
e. LympH MovEMENTS CAUSED BY VARIATION IN BLOOD-PRESSURE IN 
THE CEPHALIC VEINS AND SINUSES. 
The occurrence of large lymph-sinuses in the eyelids of Lacerta has 
been mentioned in the preceding account. Lymph-sinuses are, however, 
not confined to the eyelids. The sinuses of the lids are simply part of an 
extensive system which invades the orbit and occupies the soft tissues in 
various parts of the head. One of the largest of the orbital sinuses, 
sinus supraciliaris, communicates freely with the sinus of the upper lid. 
It hes above the bulbus, between the smooth orbital muscle and the supra- 
orbital bones. This sinus extends forward under the skin as a system of 
anastomosing spaces which gradually disappears in front of the eye. 
Posteriorly the supraciliary sinus accompanies the vena supratemporalis 
a short distance from the orbit. 
The lymph-sinus of the lower eyelid is broadly connected with an in- 
ferior orbital sinus, which lies between the smooth orbital muscle and the 
bones which underlie the lateral half of the orbit. The sinus of the lower 
lid also extends forward on the dorsal aspect of the lachrymal duct, and 
this extension is accompanied by fibers of the smooth orbital muscle, 
which le between the sinus and the skin. In a posterior direction the 
sinus of the lower lid and the inferior orbital sinus both open into a 
system of lymph-spaces which extends through the subcutaneous tissue 
of the side of the head. These spaces are especially numerous around 
the external auditory depression, from which they continue caudad into 
