338 
lu, lungs. 
lv, lens vesicle. 
m, mouth. 
ma, manus. 
mb, midbrain. 
mc, medullary canal. 
me’, tip end of medullary canal. 
md, mandibular fold. 
mes, mesoderm. 
mes’, myocardium. 
mf, medullary fold. 
mg, medullary groove. 
mk, Meckel’s cartilage. 
mp, muscle plate. 
ms, mesentery. 
mv, meatus venosus. 
mx, maxillary fold. 
myc, myoccel. 
n, nasal invagination or cavity. 
na, neural arch of vertebra. 
nc, neurenteric canal. 
nl, nervous layer of ectoderm. 
nt, notochord. 
o, ear vesicle. 
oc, optic cup. 
oe, cesophagus. 
on, optic nerve. 
os, optic stalk. 
ov, optic vesicle. 
p, pituitary body. 
pa, posterior appendage. 
pan, pancreas. 
pc, posterior cardinal vein. 
pe, pes. 
bg, primitive groove. 
bh, pharynx. 
Pl, pelvis. 
pn, posterior nares. 
The Alligator and Its Allies 
pr, pericardial cavity. 
ps, primitive streak. , 
pl, pecten. 
rt, retina. 
S, Somites. 
Sc, spinal cord. 
se, sphenethmoid cartilage. 
sf, secondary fold. 
sg, spinal ganglion. 
sm, splanchnic mesoblast. 
sn, spinal nerve. 
so, somatic mesoblast. 
si, stomodzum. 
sy, sympathetic nervous system. 
1, tail. 
ia, trachea. 
tg, thyroid gland. 
th, thickening and posterior limit 
of sf. 
in, tongue. 
to,-tooth anlage. 
tr, truncus arteriosus. 
tv, third ventricle of brain. 
tv’, third ventricle of brain. 
u, umbilical stalk. 
ul, upper lid of eye. 
ur, superior rectus muscle of eye. 
v’-"-""", first, second, and third 
cerebral vesicles. 
va, vascular area. 
vm, vitelline membrane. 
un, ventricle of heart. 
vv, vitelline blood-vessels. 
wd, Wolffian duct. 
wdo, opening of Wolffian duct. 
wr, Wolffian ridge. 
wt, Wolffian tubules. 
y, yolk. 
EXPLANATION OF FIGURES 1-26 ON PLATES VI.-XXVIII, 
All of the figures, with the exception of the photographs and those 
copied by permission from S. F. Clarke, were drawn underacameralucida. 
