The Development of the Alligator 317 
mentary, gill cleft had not Clarke (17) found a 
fifth pair of clefts in his material. The nasal 
pit has advanced in development somewhat and 
shows the beginning of the groove that connects 
it with the mouth. In this figure the crescentic 
hyomandibular cleft shows its connection with 
the groove between the mandibular and the hyoid 
folds. 
STAGE XVI 
FiGuRE 19 (PLATE XXIV.) 
This embryo is only slightly more developed 
than the preceding. Body flexure is so great that 
the forebrain and tail nearly touch. Only the 
anterior three gill clefts are visible. The maxillary 
process (mx) is longer and more narrow; the man- 
dibular fold has not changed appreciably. The 
nasal pit (7) is now connected by a distinct groove 
with the stomodeum. The appendages have 
increased in size, the posterior (fa) being the 
longer. The anterior appendage (aa) is distinctly 
broadened to form the manus, while no sign of 
the pes is to be seen at the extremity of the 
posterior appendage. The heart (ht) is still very 
prominent. Thestalk of the umbilicus (w~), which 
is quite narrow, projects from the ventral wall in 
the region between the heart and the hind legs. 
The tail is of considerable length and is closely 
coiled. 
