bserved to beat with the regularity of the pulse; but now it appears
doubled somewhat into the shape of an adult heart, although as yet it
has but one auricle and one ventricle. As time advances we find the
perfect heart with its two ventricles and two auricles, all developed
from the original straight artery. At this period the lungs appear to
exist in five or six different lobes and we can barely distinguish the
bronchial tubes; about the same time the ears and face are distinctly
outlined, and after awhile the nose is also faintly and imperfectly
perceived.

At about the _seventh week_ a little bony deposit is found in the lower
jaw. The kidneys now begin to be formed, and a little later the genital
organs. The embryo averages one inch in length.

At _two months_ the rudiments of the extremities become more prominent.
The forearm and hand can be distinguished but not the arm above the
elbow; the hand is larger than the forearm, but is not supplied with
fingers. The sex cannot yet be determined. The length of the embryo is
from one inch and a half to two inches, and it weighs from three to five
drachms. The eyes are discernible, but still uncovered by the
rudimentary lids. The nose forms an obtuse eminence, the nostrils are
rounded and separated, the mouth is gaping and the epidermis can be
distinguished from the true skin.

At _ten weeks_ the embryo is from one and a half to two and a half
inches long, and its weight is from one ounce to an ounce and a half,
the eyelids are more developed and descend in front of the eyes; the
mouth begins to be closed by the development of the lips. The walls of
the chest are more completely formed, so that it is no longer possible
to see the movements of the heart. The fingers become distinct and the
toes appear as small projections webbed together like a frog's foot. At
about this period the sexual organs show their development as follows:
On each side of the urinary locality an oblong fold becomes
distinguishable; in course of progress if these folds remain separate, a
little tubercle forms in the anterior commissure which becomes the
clitoris; the nymphae develop, the urethra forms between them, and the
female sex is determined. If, on the other hand, these folds unite into
a rounded projection the scrotum is formed, the little tubercle above
becomes the penis and hence the male sex. The testicles forming within
the body, descend later into the scrotum, and organs similar to th