Farre, on an Early Hu7nan Embryo. 
165 
tion this^ because it will explain why I am unable in this 
paper to give any account of the allantois^ which in an 
embryo of this date might be expected to present a condition 
of great interest; while, on the other hand, I am able to 
describe some points of fully equal interest, which are beau- 
tifully shown in the present example. 
The embryo, in this case, presents the elongated and almost 
snake-like form which is commonly observed in the mamma- 
lian embryo of almost all classes at the periods of develop- 
ment which correspond with this. It is slightly curved, in 
the form of a bow, the head being inclined towards the pos- 
terior extremity of the trunk. In this curved condition it 
measures four lines, but its length would be increased by 
about one fourth if it were extended. 
That which strikes the observer most at this period of 
development is the circumstance that here the embryo con- 
sists of those structures which are to be afterwards developed 
into parts and organs devoted to the purposes of what is 
termed the animal life, or those organs which bring the body 
into relation with the external world, such as the great 
centres of the nerves which relate to sensation and motion, 
the structures by which these are sustained and protected, 
the rudiments of the organs of locomotion, and some even of 
those relating to special sense, as the eye; while of those 
structures which are appropriated to the maintenance of the 
vegetative or organic life, scarcely a trace is as yet discover- 
able, beyond the heart or regulating organ of the circulation, 
v/hich, at this period of development, constitutes the almost 
sole representative of that most important series of structures. 
At this period there is neither a thoracic nor abdominal 
cavity, for, with the exception of the heart, as first stated, the 
parts which these cavities contain and protect are not yet 
formed. The entire embryo therefore consists of a trunk, 
with the rudiments of a head and limbs, and of a heart for 
the maintenance of the circulation in the structures already 
formed, as well as in the membranes in which the embryo is 
inclosed, and which serve for the supply of its nutriment and 
for the aeration of its fluids. 
It will be perceived by the drawing which accompanies this 
paper (PI. VII, fig. 8 and 9), and in which I have preserved the 
proportion of all the parts, although the entire size of the em- 
bryo is magnified about seven diameters, that the head or ante- 
rior extremity of the trunk may be readily distinguished by the 
incipient development of those great nervous ganglia, or cen- 
tres of nervous matter, which are connected in the first place 
with the principal organs of sense. 
