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 inix) is longer and more narrow; the man- 

 dibular fold has not changed appreciably. The 

 nasal pit (7z) is now connected by a distinct groove 

 with the stomodseum. The appendages have 

 increased in size, the posterior {pa) 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. The stalk of the umbilicus {it), 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. 



