|Henry Gray (18251861). Anatomy of the Human Body. 1918.|
Fourth Week.The embryo is markedly curved on itself, and when viewed in profile is almost circular in outline. The cerebral hemispheres appear as hollow buds, and the elevations which form the rudiments of the auricula are visible. The limbs now appear as oval flattened projections (Fig. 60).
FIG. 61 Human embryo, thirty-one to thirty-four days old. (His.) (See enlarged image)
Fifth Week.The embryo is less curved and the head is relatively of large size. Differentiation of the limbs into their segments occurs. The nose forms a short, flattened projection. The cloacal tubercle is evident (Fig. 61).
FIG. 62 Human embryo of about six weeks. (His.) (See enlarged image)
FIG. 63 Human embryo about eight and a half weeks old. (His.) (See enlarged image)
Sixth Week.The curvature of the embryo is further diminished. The branchial groovesexcept the firsthave disappeared, and the rudiments of the fingers and toes can be recognized (Fig. 62).
Seventh and Eighth Weeks.The flexure of the head is gradually reduced and the neck is somewhat lengthened. The upper lip is completed and the nose is more prominent. The nostrils