Henry L. Bruner 53 
are commonly considered as belonging to the vagus. It is very probable 
that a similar relation exists in other forms in which the constrictor 
muscle occurs. 
In the lizard the motor fibers of the tumefactor nerves are relatively 
small, resembling those of the vagus trunk, while the chief motor branch 
of the accessorius (ramus externus accessori1) is composed of very large 
fibers. 
The relations ef the constrictor muscle, especially its attachment to 
the second epibranchial cartilage, suggests its derivation from a branchial 
muscle of the second arch, which in lower forms is supphed by the 
vagus nerve. 
3. ONTOGENY AND PHYLOGENY OF THE M. CONSTRICTOR VENA JUGU- 
LARIS INTERN#.—The embryological development of the constrictor 
muscle begins a little later than that of the other striated muscles of the 
head. In a Lacerta embryo with head 1700 » long no trace of the con- 
strictor fibers could be seen, although the fibers of other muscles had 
begun their development. In Sceloporus the formation of the primitive 
fibers begins with a head-length of about 1900 ». In a specimen with the 
head 2100 » long the development of the fibrille in the periphery of the 
fibers has begun. In a later stage, head 2500 » long, the number of 
fibers has considerably increased and the development is well advanced. 
In both Sceloporus and Lacerta the muscle fibers are fully formed at 
the time of hatching. 
According to the above account the fibers of the m. constrictor ven 
jugularis interne arise in place; they are not cut off from one of the 
larger adjacent muscles. This observation indicates that the constrictor 
muscle is not a recent acquisition but has been derived, by modification 
and change of function, from an earler muscle which occupied a closely 
related position. 
The probable character and function of this primitive muscle are sug- 
gested by a study of the branchial muscles of the lower amphibians. All 
Perennibranchiata, Derotremata, and Coecilia are provided with a sys- 
tem of muscles which arise from the parotic region of the head and 
insert on the dorsal ends of the cartilaginous branchial arches (mm. 
levatores arcuum of Fisher, 54). According to Hoffmann, 73-78, there 
are four pairs of these muscles in Siren, three pairs in Proteus, Necturus, 
Cryptobranchus, and Amphiuma. Homologous muscles also occur among 
the Salamandrida (Coghill, 02). 
In accordance with the close relation which exists between the glos- 
sopharyngeus and vagus nerves in the Urodela, the mm. levatores arcuum 
