Henry L. Bruner 105 
the spongy body of the higher forms is a relic of the moulting mechanism 
of reptile-like ancestors. The survival of the spongy body in the higher 
group, and also in the Crocodilia, may be easily explained by the develop- 
ment of arrangements for local control. It will be remembered that we 
found abundant evidence of such control of the spongy body in the lizards. 
C. PHYLOGENY OF THE SINUSES. 
The phylogeny of the venous sinuses of the reptilian head is indicated, 
in a general way, by their ontogeny. Somewhere along the line of de- 
scent of the modern reptiles ordinary veins and capillaries were en- 
larged to form the sinuses of the swell mechanism. The chief factors in 
this phylogenetic development were presumably the following: 
1. The muscle mechanism which raised the blood-pressure in the 
cephalic veins by obstruction of the vena jugularis interna. At the time 
the sinuses were formed this mechanism probably included a single 
special muscle, the m. constrictor vene jugularis interne. 
2. Cardio-accelerator and vaso-motor mechanisms, which increased the 
flow of blood to the head and thus contributed to the elevation of the 
venous blood-pressure. 
3. Heredity. 
The most important of these factors was undoubtedly the muscle 
mechanism. Comparison of living species, such as Lacerta and Phryno- 
soma, shows that the abundance and size of the sinuses correspond 
directly to the efficiency of the constrictor muscle, and this was probably 
true, also, in all stages of the phylogenetic development. When, for 
any reason, the muscle mechanism dwindled and disappeared, the sinuses 
disappeared also. This explains the absence or reduction of the sinuses 
in Platydactylus, Chameleon, and Rhineura, in which the muscle 
mechanism for elevating the venous blood-pressure has been partly or 
wholly lost. 
VI. COMMENT. 
1. The swell mechanism of the lizards offers a partial solution of the 
problem concerning the ejection of blood from the orbit of the “ horned 
toad,” Phrynosoma. The sinus orbitalis forms a suitable reservoir for 
the reception of the blood to be ejected. This sinus may be filled with 
blood by contraction of the m. constrictor vene jugularis interne. The 
m. protrusor oculi could probably furnish sufficient force to cause the 
ejection of the accumulated blood, but if necessary, this muscle might be 
assisted by the smooth muscle of the orbit, m. compressor sinus orbitalis. 
