Page:Laboratory Manual of the Anatomy of the Rat (Hunt 1924).djvu/128

114 tor foramen of the coxal bone to the adjacent muscles. The sciatic nerve may be traced from the lumbar plexus to the deeper posterior muscles of the thigh.

The remainder of the fifth lumbar nerve, and the sixth lumbar nerve, together with part of the first and second sacral nerves, form the sacral plexus. There are four pairs of sacral nerves. Locate the caudal nerve in the tail and trace it forward to its connections with the sacral nerves.

Exercise XXX. Sketch the spinal and sympathetic nerves of one side of the body.

Clear away the muscles surrounding the backbone and sever the head from the body at the articulations between the cranium and the atlas. Carefully expose the spinal cord throughout its length by removing the roof of each neural arch. The cord is surrounded by tough membranes, the meninges.

Observe the connections of several of the spinal nerves with the cord. Each nerve proceeds from the cord as a pair of roots, a dorsal and ventral. The former bears a swelling, or ganglion. Trace a pair of roots from their origin to the point where they unite to form the spinal nerve. The dorsal ganglia in mammals contain the cell bodies of sensory neurons which send some of their fibers through the dorsal root to the spinal cord, and other fibers distally to the spinal nerve. The dorsal root is, therefore, sensory in function. The ventral root carries motor fibers from nerve cells located in the cord itself. Thus each spinal nerve carries nervous impulses both to and from the spinal cord.

Observe the cervical and lumbar enlargements of the cord in the neck and lumbar regions, respectively. The