64 GENERAL EMBRYOLOGY. 
By the end of the third week Wolftian ridges appear below the ventral ends of the 
protovertebral somites; they are most marked in the thoracic and pelvic regions, where 
, 
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Fic. 50. 
G. Human embryo at the 29th day of development ; H. At the 32nd day of development. (After His.) 
KE. Rudiment of ear; EY. Eye; FL. Fore-limb ; HA. Hyoid arch ; HL. Hind-limb ; MA. Mandibular arch ; 
MB. Mid-brain; MP. Maxillary process; OP. Olfactory pit ; PR. Pericardial region ; UC. Umbilical 
cord, 
bud-like projections form the rudiments of the limbs. Four visceral clefts are visible, and 
there is a distinct tail. 
The fourth week.—The embryo is curved upon itself, and its outline is almost 
Fic. 51.—HuUMAN Farus AT THE SIXTH WEEK Fic. 52.—HUMAN F@TUS SIX AND A 
oF DEVELOPMENT. (After His.) HALF WEEKS OLD. (After His.) 
D. Digits ; EE. Rudiment of ear; FL. Fore-limb ; HL. Hind-limb ; MP. Maxillary process ; N. Nose ; 
UC. Umbilical cord. 
circular. The visceral arches begin to overlap each other. The rudiments of the external 
ear are just visible as small nodules. The limb rudiments are flat, oval buds. 
The fifth week.—The curvature is diminished, and the head and neck form about 
