110 The Cephalic Veins and Sinuses of Reptiles 
pressure runs through all of the veins and sinuses which are tributary 
to the sinus orbitalis. 
7. The stage of reduction is inaugurated by relaxation of the m. con- 
strictor ven jugularis interne, the m. protrusor oculi, and the bucco- 
pharyngeal muscles. The reduction of blood-pressure is followed by a 
slowing down of the heart-beat, probably, also, by constriction of the 
carotids and dilation of the posterior arteries. 
8. In the Sauria the swell mechanism is a moulting mechanism. It 
facilitates exuviation (a) in a physiological way, by accelerating the 
movement of the lymph and promoting the processes of metabolism; (b) 
in a mechanical way, by stretching the skin which covers the soft parts 
of the head. . 
The swell mechanism probably has the same function in the Sauria, 
Ophidia, and Testudinata. 
9. In the Sauria the moulting mechanism may be set in motion by 
artificial stimuli, such as court plaster or mucilage, whose application to 
the head is followed by the same response that is observed under natural 
conditions. 
10. The operation of the moulting mechanism is more or less reflex, 
but it may also be brought under voluntary control. If conditions are 
unfavorable for its operation. the movements may be suppressed alto- 
gether. 
11. The existence of the moulting mechanism in the Sauria and other 
reptiles is justified, first, because of the difficulties accompanying exuvia- 
tion in the head; second, because of the demand for a prompt removal 
of the old stratum corneum from the openings of the sense organs. 
12. In view of its distribution among modern reptiles, we may con- 
clude that the moulting mechanism has been inherited from pro-reptilian 
forms which became the ancestors of all true reptiles, both ancient and 
modern. It is probable that the moulting mechanism was widely dis- 
tributed among extinct reptiles. 
13. The first development of the moulting mechanism probably oc- 
curred in transitional forms which were intermediate between amphibians 
and reptiles. The development was probably correlated with a thicken- 
ing of the epidermis and the loss of cutaneous glands, the moulting 
process becoming more difficult on account of these changes. 
14. The spongy tissue which occurs in the nasal vestibule of crocodi- 
lians and in the region of the inferior turbinate bone of mammals is 
probably a relic of the moulting mechanism of lower forms. 
