Bauhaus-Universität Weimar

868* 
DEVELOPMENT OP THE EMBRYO. 
like prominence in front of the cleft which leads to the sinus urogenitalis. The urinary 
bladder is formed at a later period by a part of the sinus just named, leading in the direction 
of the urachus, being separated from the rest by a constriction. At this time the oral and 
nasal cavities are not separated; the eyelids and external ear, however, are beginning to be 
formed; the different parts of the extremities become perceptible, and the hands and feet 
present marks of the division into the digits. The embryo is now about one inch in length. 
In the course of the third month the foetus acquires the length of two and a half or three 
inches; in the fourth, during which the sex becomes distinguishable, it reaches to four inches; 
and in the fifth to twelve inches. At this period occur the formation of the fat, and the 
further development of the rudimentary horny structures, the nails and the down, lanugo, 
which appears over the whole surface, and the eyelids coalesce. In the fifth month, also, 
the movements of the embryo are felt by the mother. A fetus born during the sixth month 
breathes, but does not continue to live. In the seventh lunar month, the embryo acquires the 
length of 16 inches or more, and if expelled from the uterus is sometimes capable of living; 
its skin is red. In the eighth lunar month its length is 16| inches; the testes at this period 
descend from the abdominal cavity through the inguinal ring into the scrotum, which had 
hitherto the form of empty folds of skin, and the eyelids become free. In the ninth month 
the hair appears on the head, and the embryo measures 17 inches in length. In the tenth 
lunar month its length reaches 18 or 20 inches. At this period, or even during the eighth 
or ninth month, the membrana pupillaris disappears; and the skin, no longer so red, is 
covered by an unctuous matter, the “ vernix caseosa,” which, according to R. Wagner, con¬ 
sists of the desquamated scales of epidermis. In other animals the skin seems to throw off 
the epidermis in the form of a continuous membrane, and hence the body of the embryo has 
been frequently seen enveloped in this free epidermal membrane, whilst the hairs which had 
been formed subsequently were growing beneath it.
        

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