110 ANTHROPOLOGY. 
nervous system. This we shall consider under the heads of the spinal cord 
and of the brain or encephalon, the latter including the medulla oblongata, 
the mesocephalum, the cerebellum, and the cerebrum. 
B. The Spinal Cord. 
The spinal cord occupies a large portion of the spinal canal, terminating 
inferiorly at a point, which in different subjects ranges between the last 
dorsal and the second lumbar vertebra. Below this point, the sheath 
formed by the dura mater contains that series of nerves known as the cauda 
equina. ‘The entire length in the adult is from sixteen to eighteen inches. 
Its circumference measures twelve lines at the smallest, and erie at the 
most voluminous part. Its weight is said to be Soil the ;', to the > or 
that of the brain in the adult, and about the ;, part in the new-born inte. 
The actual weight of the peel cord in the adult may be taken at a little 
over one ounce. | 7 
The consistence of the medullary substance of the spinal cord, when fresh, 
is much greater than that of the brain. The pia mater adheres very closely 
to its surface, like neurilema to a nerve. It is penetrated both on the an- 
terior and posterior aspect by fissures, each of which corresponds to the 
median plane. They are separated from each other by a transverse bilami- 
nate partition of white and grey matter, of which the grey layer is posterior. 
This serves to connect the equal and symmetrical portions into which the 
cord is divided by these fissures. The anterior of these fissures is deeper 
than the posterior. The two taken together seem to indicate the existence 
of two spinal cords, one for each side of the body, both presenting a perfect 
resemblance in Ae and structure. ° 
On examining a transverse section of the spinal cord, we find that the 
interior of each lateral portion is occupied by grey matter disposed in a 
erescentic form, exactly similar in each, and connected by the grey com- 
missure, a layer which extends between the two crescents, being attached 
nearly to the central point in each. This commissure forms a vertical plane 
of grey matter throughout the whole of the cord. The concavity of the 
lateral crescent is directed outwards. Their anterior extremities are thick, 
and separated from the surface of the cord by a considerable layer of white 
fibrous matter. The posterior extremities of the crescents are prolonged 
backwards and outwards in the form of a narrow horn, which reaches the 
surface of the cord. These posterior horns constitute on each side a natural 
boundary, between the two columns of which each lateral half of the cord 
consists. All in front of the posterior horns is called the antero-lateral 
column, comprehending the white matter forming the sides and front of the 
semi-cord, limited anteriorly by the anterior fissure, and posteriorly by the 
posterior roots of the nerves. The posterior column is situated behind the 
posterior horn of grey matter, and is separated from its fellow on the oppo- 
site side by the posterior fissure. 
There are these four columns in the spinal cord, two antero-lateral and 
two posterior. The-former constitute by far the larger proportion of the 
white substance of the cord, and they envelope the anterior obtuse portion 
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