150 



THE HUMAN EMBRYO. 



mid-brain finally directly above the hind-brain, the embryo being con- 

 ceived as having the body vertical. During the elevation of the head the 

 concavity (N ackengrube] at the back of the neck is gradually obliterated. In 

 both head and rump the external modeling, which in earlier stages indicated 

 more or less the position of the internal organs, has become blurred, and in the 

 next stage is found to have nearly or quite disappeared. The maxillary pro- 

 cesses have met and united in the median line. The anlages of the eyelids have 

 developed. The concha of the ear is indicated. The arm reaches beyond the 

 heart; the fingers appear as separate outgrowths. 



Fifty Days. Embryo of 21 mm. The author has a fair specimen which 

 came into his possession with no history whatever, but it agrees very closely 



with His's embryo Ltz, of which he fixes 

 the probable age as just over seven weeks. 

 The head is nearer its final position than 

 in figure 88, and relatively larger in pro- 

 portion to the body. In the eye, cornea 

 and conjunctiva are clearly separated ; the 

 face has the foetal form, the nose, mouth, 

 and chin being fully marked off. The 

 arms are clearly divided into upper and 

 lower segments; the five digits are well 

 developed ; the hands rest over the heart 

 and nearly touch one another. In the 

 specimen figured the outline of the abdo- 

 men is abnormal. The leg shows the 

 tripartite division ; the toes are just begin- 

 ning to be free, but the hind-limb is much 

 less advanced than the fore-limb. The 

 tail is still a freely projecting appendage. 



Fifty-three Days. Embryo of 22 mm. The specimen (Fig. 89) is probably 

 not quite normal, but, except for the extreme and unusual curvature of the 

 back, it agrees closely with His's embryo Zw, which is figured by him as a 

 normal embryo of presumably about seven and one-half weeks. The specimen 

 was received in 1884 with the following history: " Menstruation began January 

 26th. February and March slight show every few days. Abortion March 

 3oth," which is insufficient to determine the age. As compared with the last 

 stage, there are comparatively few changes of external form ; the most note- 

 worthy are perhaps the increased development of the legs and feet and the 

 commencing disappearance of the free tail. At this time the protrusion of the 



FIG. 89. HUMAN EMBRYO OF 22 MM. 

 diatns. 



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