148 



TEXT-BOOK OF EMBRYOLOGY. 



cervical depression is deeper, and the neck region in general is fairly well 

 differentiated. 



The ventral part of the first branchial arch has fused with the ventral part 

 of the second, leaving the dorsal part of the first groove open to form the ex- 

 ternal auditory meatus. The parts surrounding the meatus bear more resem- 

 blance to the concha of the ear. The mandibular process of the first arch has 

 become differentiated in part into the lower lip and chin regions. The ventral 

 (distal) end of the maxillary process represents the region of the upper lip. The 



FIG. 126. 



FIG. 127 



FIG. i26.-Human embryo of 15.5 mm. (39-40 days) His. 

 . 127. Human embryo of 16 mm. (42-45 days;. His. 



nose is apparent as a short process extending from the fore-brain region toward 

 the upper lip. 



The limb buds are turned more nearly at right angles to the long axis of the 

 The radial depressions which were present on the flattened distal por- 

 on of the upper limb in the preceding stage are now continuous with depres- 

 sions around the distal border. Similar radial depressions are also present on 

 the distal portion of the lower limb. The tail is smaller in proportion to the 

 rest of the embryo. 



