92 The Cephalic Veins and Sinuses of Reptiles 
phylogenetic relation of the two groups, it is reasonably certain that 
the Ophidia, as well as the Sauria, employ blood-pressure as an aid to 
exuviation. The great development of blood-vessels which Hyrtl, 38, 
found in the preocular curtain of snakes at the moulting time may be 
intimately associated with the high blood-pressure caused by obstruction 
of the vena jugularis interna. 
The relative simplicity of the moulting mechanism in the Ophidia 
evidently corresponds to the character of the work to be done. On ac- 
count of the union of the eyelids, and because of the absence of an 
external auditory depression, the moulting of the head is less difficult 
than in the Sauria. Moreover, in the snake the movements of the facial 
bones and suspensorium of the jaws must facilitate exuviation in a 
mechanical way and thus relieve the moulting méchanism of a part of 
its work. The details of the process must yet be verified, however, by a 
study of the moulting animal. As yet only the final stage has been 
observed. 
This stage has been briefly described by Sharp, 90, who made his ob- 
servations on two specimens of the American garter snake, Hutenia 
sirtalis Linnaeus. These animals immersed themselves in water some 
time before the final stage began. The removal of the exuvize occurred 
immediately after the snakes left the water. By pressing the head into 
a narrow opening the skin was parted along the lips. The two flaps of 
skin were then turned backward above and below the head, and the ani- 
mals crept forth, turning the skin inside out. The entire process occu- 
pied less than a minute and in one case the skin was removed without 
tearing. This is probably the typical mode of removing the old stratum 
corneum in the snakes. 
Under normal conditions the moulting process is repeated at somewhat 
regular intervals. Thus, Gunther, 98, reports the following observa- 
tions on the exuviation of Indian snakes kept in the Madras museum: 
Python molorus moulted April 12, July 2, December 17. 
Zamenis mucosus moulted April 22, May 18, June 15, July 8, August 
18, September 5, October 5, November 7, December 14, 1896; January 
17, February 27, 1897. 
Tropidonotus stolatus moulted June 28, July 6, July 27, September 3, 
December 14, 1896; January 18, February 27, 1897. 
Dendrophis pictus moulted April 2, May 6, June 26, July 27, October 
29, 1896; died January 22, 1897. 
