672 The Significance of Human Anomalies. [November, 
carotid, and so supplies both sides of the head, the artery 
supplying the left arm coming off as usual. This is the 
normal condition in apes, bears, dogs, and all the feline 
tribe. In some rare cases in man one branch only comes 
off from the aortic arch, and this, again, divides into the 
various arteries supplying the head and arms. In horses 
and other solipeds we see this form of aortic arch. Again, 
the branches may all be given off separately from the arch, 
as is the arrangement in the walrus. 
I have three times met with rather a rare anomaly of the 
great veins going to the heart from the upper part of the 
body. 1 he usual arrangement in man, on each side, is for 
the great vein of one arm and the corresponding side of the 
head to unite and form a single trunk (brachio-cephalic), so 
we have two large venous trunks, one on each side ; these 
two trunks then join to form a single large vessel, called the 
superior vena cava, which empties its blood into the right 
side of the heart. It occasionally happens that the great 
venous trunks formed by the veins of the arm and head of 
each side do not unite to form the superior vena cava, but 
each continues its downward course and opens separately into 
the heart. On studying the development of the blood- 
vessels we find that in early foetal life this condition of 
affairs exists, but after a time a transverse branch forms be- 
tween the two trunks. This branch gradually enlarges, 
while the left trunk shrivels up, and at birth is only repre- 
sented by a fibrous cord. This anomaly of the veins we 
find, then, is a persistence of a usually transient foetal con- 
dition in man, and also that in all birds and many of the 
lower mammals it is the permanent condition. 
Muscular System . — The muscular system of man is liable 
to many variations, nearly all of which are interesting from 
a morphological point of view. 
It is not uncommon to find in man useless rudiments of 
muscles which exist in a well-developed state in some of 
our more humble fellow-creatures, and in them serve a 
definite purpose. 
In man the “ skin-muscles ” are very feebly developed 
compared with those seen in many of the lower animals. 
The only remnants of these in man are, — the muscle which 
wrinkles the forehead ( occipitofrontalis ), the muscle imme- 
diately under the skin covering the side of the neck ( platysma 
myoides), and the palmaris brevis, a little bundle of muscular 
fibies in the palm of the hand ; not unfrequently remnants 
appear abnormally in other situations, as over the breast, in 
