HUMAN EMBRYO AT DIFFERENT STAGES. 65 
half the embryo. The eye is recognisable externally. The nose begins to grow forwards, 
but it is still broad and flat, and the nostrils are widely apart. The nodular elements of 
the external ear fuse together. The segments of the limbs are defined, but the digits do 
not project beyond the ends of the limb-buds. The genital tubercle, the rudiment of the 
external generative organs, is formed. 
The sixth week.— During the sixth week the increase in size is less rapid than in 
previous stages, but the embryo begins to assume a more distinctly human form. The 
head remains relatively large and it is bent at right angles to the body. The neck is 
better defined and appears as a constricted region between the head and trunk. The 
maxillary processes fuse with the lateral nasal processes, and the lips and eyelids begin to 
assume their characteristic form. The outer parts of all the visceral clefts except the 
hyo-mandibular disappear. The external ear acquires its adult form. The rotation of 
the limbs commences, and the fingers reach the extremity of the hand; the tail is 
beginning to disappear as an external projection. 
The seventh week.—The flexure of the head upon the body is reduced. The nose 
projects more than in the preceding stage, and the chin appears. The toes reach the 
margins of the feet, and the projecting portion of the tail is still further reduced in 
length. 
The eighth week.—The flexure of the head disappears. The forehead projects. 
The nose narrows and becomes more prominent, but the anterior nasal orifices are still 
directed forwards. The upper lip is completed 
by the fusion of the globular processes. The 
thumb is widely separated from the fingers, and 
the hand assumes a distinctly human appearance. 
The tail is reduced to a small nodule, and the 
umbilical cord is attached to the lower part of 
the abdominal wall. At the end of the second 
month the total length of the foetus, excluding 
the legs, is 28 mm. (14 in.). 
The third month.—The head grows less 
rapidly and, though it is still large, it is rela- 
tively smaller in proportion to the whole body. 
The eyelids close, and their margins fuse to- 
gether. The neck increases in length. The 
various parts of the limbs assume their 
definite proportions, and nails appear on the 
fingers and toes. The proctodzeum is formed and 
the external generative organs are differentiated, 
so that the sex can be distinguished on external 
- examination. The skin is a rosy colour, thin 
and delicate, but more consistent than in the 
preceding stages. By the end of the third 
month the total length of the foetus, excluding 
‘ the legs, is 7 cm. (24 in.), including the legs, 
| 9-10 cm. (332-4 in.), and it weighs from 100-125 
lee lid 
grammes (34-44 02.). 
The fourth month.—In the fourth month 
the skin becomes firmer, and fine hairs are 
developed. The disproportion between the 
fore and hind limbs disappears. If the foetus 
is born at this period it may live for a few 
hours. Its total length from vertex to heels — Fic. 53,—HumaN F@rTus BIGHT AND A HALF 
is 16-20 cm. (62-8 in.), from vertex to coccyx WEEKS OLD. (After His.) 
12-13 cm. (44-51 in.), and it weighs from 230- GE. Genital eminence ; UC, Umbilical cord. 
260 grammes (81-91 o7.). 
The fifth month.—The skin becomes firmer, the hairs are more developed, and 
sebaceous matter appears on the surface of the body. The legs are longer than the arms, 
and the umbilicus is further from the pubis. At the end of the month the total length 
of the foetus, from vertex to heels, is 25-27 cm. (10-104 in.), from vertex to coceyx 20 cm. 
(8 in.), and its average weight is about half a kilogramme (1,15 lbs.). 
The sixth month.—The skin is wrinkled and of a dirty reddish colour. The hairs 
are stronger and darker. The deposit of sebaceous matter is greater, especially in the 
axillee and groins. The eyelashes and eyebrows appear. At the end of the month the 
