102 The Cephalic Veins and Sinuses of Reptiles 
phology and physiology and has already been assumed in the earlier 
part of this paper. If this view is correct, we must conclude that the 
swell mechanism of the modern Sauria, Ophidia, and Testudinata has 
been inherited from common ancestors. It is, therefore, in order to show 
that this view is entirely in accord with the evidence furnished by 
phylogeny. 
Paleontologists tell us that the lines of descent of the Sauria, Ophidia, 
and Testudinata meet in generalized forms of paleozoic age, from which 
all of the reptilian orders, both recent and fossil, have been derived. The 
probable relations of these orders, as interpreted by Fiirbringer, 00, may 
be represented by the following diagram: 
Sauria 
Mosasauria Ophidia 
Rhynchocephalia Squamata Ichthyopterygia 
Mesosauria Tocosauria Dinosauria 
Testudinata Patagosauria 
Sauropterygia Theromorpha Crocodilia 
Synaptosauria Archosauria 
= Tae Mop 
Pro-reptilia 
(hypothetical) 
From these and similar views, which are advocated by Zittel, 87-90, 
Cope, 98, Lydekker, 88, 89, Osborn, 04, and others, we may conclude 
that the swell mechanism was already fully developed in pro-reptilian 
forms which became the ancestors of all the various orders of reptiles. 
According to the evidence of paleontology these primitive reptiles were 
lizard-like forms, which were provided with a scaly skin and a thick 
epidermis. Is is probable, also, that they moulted the stratum corneum 
in true saurian fashion, utilizing the swell mechanism to accelerate the 
process. 
If the foregoing views are correct, the origin of the moulting mech- 
anism must be sought among the ancestors of the pro-reptilia. It is 
reasonably certain that the latter were descended from amphibians, 
probably from the Stegocephala, from which, also, they inherited 
the moulting habit. We may, perhaps, assume that the demand for 
such a mechanism first arose in that transition period when these an- 
