men in the neural arch of the atlas. The other seven pairs escape through the intervertebral foramina. The first, second, third, and part of the fourth pairs of nerves go to the neck muscles. The phrenic nerve leaves the fourth cervical nerve. Trace it caudad to the diaphragm.
Dissect the brachial plexus, the conspicuous bundle of intercommunicating nerve trunks in the axillary region. It is formed by the fourth, fifth, sixth, seventh, and eighth cervical, and the first dorsal nerves. Note the size of these nerves. The brachial plexus sends the following branches to the arm, (1) The ulnar nerve goes to the posterior region of the forearm. (2) The median nerve runs across the anterior surface of the elbow joint, supplying the muscles of the inner side of the arm. (3) The axillary nerve passes around the posterior side of the humerus, crosses the elbow joint, and as the radial nerve proceeds to the outer side of the arm. Locate, also, the branches going from the plexus to the thorax.
There are thirteen pairs of thoracic spinal nerves. The first enters the brachial plexus. The second to the twelfth inclusive run in the muscle tissue between the ribs. The thoracic nerves leave the spinal canal through the inter-vertebral foramina. Except for the first, they innervate the walls of the thorax and anterior part of the abdomen.
The six pairs of lumbar nerves are associated with the thick muscle masses in the lumbar and sacral regions. Carefully remove these muscles without severing the nerves or their connections. The first two pairs of lumbar nerves innervate the abdominal walls, by way of the lumbar plexus. Find the lumbar plexus, which is formed on each side by part of the first, second, third, fourth, and fifth lumbar nerves. The three following nerves arise from it. The femoral nerve proceeds caudally to the inner aspect of the hind limb. The obturator nerve passes through the obtura-
