Henry L. Bruner 99 
V. DISTRIBUTION AND PHYLOGENY OF THE SWELL 
MECHANISM. 
In the preceding pages I have described a peculiar swell mechanism 
in the head of certain reptiles, including representative species of Sauria, 
Ophidia, and Testudinata. This mechanism is used by the Sauria for 
moulting purposes, and it probably performs the same function in the 
other orders. I now wish to review the taxonomic relations of the 
species studied and to show, as far as possible, the character and distri- 
bution of the swell mechanism in the suborders and families of modern 
reptiles. Afterward, the phylogenetic relations of the different reptilian 
orders will be considered and an effort will be made to determine the 
phylogeny of the swell mechanism and its probable distribution among 
extinct orders. 
A. DISTRIBUTION OF THE SWELL MECHANISM AMONG 
MODERN REPTILES. } 
The general characteristics of the swell mechanism has been deter- 
mined in representative species of the following orders, suborders, and 
families of reptiles: 
a. SAURIA. 
1. RHIPTOGLOSSA.—Chameleontide. Chameleon vulgaris Cuvier. The 
m. protrusor oculi is present; the m. protrusor oculi accessorius and m. 
constrictor ven jugularis interne are wanting. Blood sinuses are well 
developed in the anterior part of the head and in the cranial cavity. 
Extracranial veins are little enlarged in the posterior part of the head. 
2. PACHYGLOSSA.—A gamide. Agama colonorum Daudin, Moloch hor- 
ridus Gray. The m. constrictor vene jugularis interne and m. pro- 
trusor oculi are present; the m. protrusor oculi accesorius is wanting. 
Iguanide. Anolis caroliniensis Cuvier, Sceloporus undulatus Latreille, 
Phrynosoma cornutum Harlan. 
The muscles are the same as in the Agamide. 
3. NYCTYSAURA.—Geckonide. Platydactylus mauritanicus Linnaeus. 
M. protrusor oculi and m. protrusor oculi accesorius are present. The 
m. constrictor ven jugularis interne is wanting. The sinus orbitalis, 
sinus palatinus, and sinus vestibuli nasi show about the same development 
as in other forms. The veins of the postorbital part of the head are little 
enlarged, excepting those of the cranium and certain others that are con- 
nected with the cranial vessels. 
