ZOOLOGY: E. P. ALUS 
73 
arrangement favorable to the particular curve or form of the stem 
imposed by the neuromuscular response. The work thus briefly re- 
ported upon was carried out last summer at the Scripps Institution 
for Biological Research, to the staff of which the writer is indebted 
for many courtesies. 
1 Contributions from the Zoological Laboratory of the Museum of Comparative Zoology 
at Harvard College, No. 287. 
THE LIPS AND THE NASAL APERTURES IN THE GNATHOSTOME 
FISHES, AND THEIR HOMOLOGUES IN THE HIGHER 
VERTEBRATES 
By Edward Phelps Allis, Jr. 
PALAIS CARNOL^S. MENTON, FRANCE 
Communicated by E. L. Mark, December 12, 1916 
Two distinctly different types of upper and lower lips, and a third 
type of upper lip are found in the gnathostome fishes, and they may 
be called the primary, secondary and tertiary lips. 
The primary lips lie immediately external to the dental arcades devel- 
oped in relation to the palatoquadrates and mandibulae, and they 
must, because of this position, have primarily lain but slightly, if at 
all, anterior to the oral plate of embryos. The primary cavity of the 
mouth lies internal to these lips. The hypophysial invaginations prob- 
ably lay external to them, as they actually do lie external to the upper 
and primary lip of Petromyzon, and to both the primary and secondary 
upper lips of Amia and Acipenser. 
The secondary lips of either side lie external to the primary ones, 
and have been developed from what was primarily simply a fold of the 
external dermis that lay posterior to the angle of the gape of the pri- 
mary lips. The pressure of the musculus adductor mandibulae, where it 
passed around the angle of the primary gape, caused this fold to bulge 
forward across that angle, and its anterior surface was then presented 
antero-mesially. The crest of this fold then formed a secondary angle 
of the gape, which lay antero-lateral to the primary angle, and short 
secondary lips ran forward from it, in either jaw, to join the primary 
lips. These primarily short secondary lips then gradually extended for- 
ward in either jaw and ultimately there reached the median line and 
coalesced with their fellows of the opposite side, a band of the external 
surface of the head, lying between these secondary lips and the primary 
ones, thus being enclosed in the cavity of the mouth as a secondary 
