50 THE FROG 
form and in the appearance of the cytoplasm. Sketch a small 
porcion of connective tissue. 
XVI. THe NERvous SYSTEM. 
A, General Anatomy.—The nervous system is composed of two 
great divisions, the central and the peripheral. The central 
nervous system includes the brain and the spinal cord; the 
peripheral system includes all the nervous structures outside the 
cord: the cranial, spinal and sympathetic nerves, and various 
small ganglia. The system of nerves and ganglia which supplies 
the viscera is sometimes considered separately as the sympathetic 
nervous system, and in distinction from it all the rest of the 
nervous system is called the cerebro-spinal nervous system. 
1. The central nervous system. The method of making the 
following dissection will be demonstrated at each table, but each 
student should do the work on his own specimen. Expose the 
brain and spinal cord as follows: Remove the skin from the dorsal 
surface of the body, and dissect away the muscles which cover 
the vertebrz; then cut through the tough membrane roofing over 
that portion of the brain between the skull and the first vertebra, 
taking care not to injure the brain. Through the opening thus 
made introduce one blade of a pair of strong scissors and cut 
away the roof of the cranium. This is best done by making a 
forward incision through the roof of the cranium on each side of 
the brain, then with forceps removing the piece between these 
two cuts. Working backward from the same starting-point, in 
like manner remove the roof of the spinal canal, in which the 
cord lies, by cutting through the neural arches of the vertebre. 
Observe that the cord possesses two enlargements, the anterior 
or brachial and the posterior or lumbar enlargement. Behind 
the lumbar enlargement the cord gradually tapers to a point. 
Observe the dorsal longitudinal fissure. Carefully cut down the 
stumps of the neural arches and expose the roots of the spinal 
nerves. As these roots pass through the intervertebral foramina 
they are surrounded by the dense, white calciferous bodies or 
so-called periganglionic glands, each of which, as the latter 
name implies, encloses a spinal ganglion. The calciferous bodies 
are not glandular in nature, but represent extensions of the 
