Oo 
Henry L. Bruner 
the orbit, but if such a mechanism exists, is the ejection of blood its chief 
function or an accessory one? If the latter is true, what is the chief 
function and does the mechanism occur in other forms which do not eject 
blood? To answer these questions in a satisfactory way it is evident 
that we must study not only the arrangement of blood-vessels but also 
their relation to the other structures of the head. 
The present study is an attempt to solve these problems and others 
which they suggest. In the first part of the paper I shall describe the 
veins and sinuses of the head, particular attention being given to the 
Sauria. In the second part I shall show that the sinuses are always 
associated with a special mechanism for obstructing the vena jugularis 
interna and elevating the venous blood-pressure in the head. Different 
modifications of this mechanism will be found in the different orders of 
reptiles. 
In regard to the functions of this mechanism, I shall show, from obser- 
vations on lizards, that it plays an important part in exuviation—a pro- 
cess of vital importance to these reptiles. Finally, an effort will be made 
to trace the phylogenetic history of this moulting mechanism, to discover 
the conditions which determined its development and the causes of its 
preservation in certain groups and its disappearance in others. 
In order to obtain the most satisfactory results the investigation has 
been confined chiefly to adult forms, in which final conditions are fully 
established. The anatomical descriptions are based largely on serial 
sections, but the results have been corrected as far as possible by means 
of gross dissections. The material used for the sections was injected 
with an aqueous solution of Berlin blue, fixed in formalin and decalcified 
by means of phloroglucin. The acid was neutralized on the slide by 
immersion in a saturated solution of ammonium chloride. The cutting 
was done chiefly with a large Jung microtome, and in spite of the size 
of some of the heads, which included Emys and Phrynosoma, excellent 
series were obtained. 
The studies leading up to the present paper have been prosecuted for 
the most part in the Biological Laboratory of Butler College. <A part 
of the sections, including Monitor, Agama, Platydactylus, and Moloch, 
were prepared by the author in the Anatomical Institute of Professor 
Wiedersheim, of the University of Freiburg, to whom he is greatly 
indebted for the material and for valuable suggestions in regard to 
literature. 
