DR. J. MURIE ON THE FORM AND STRUCTURE OF THE MANATEE. 185 
the first, has its exit from the same foramen as the third—namely, betwixt the second 
and third cervical vertebre; but it lies posterior to the tiny second tendon of the 
scalenus. It joins outwardly the fifth nerve. The above four roots may be regarded 
as constituting the cervical plexus. 
Of the nerves forming the brachial plexus, the fifth is of considerable calibre, and 
issues between the scalene tendons, marking the third and fourth cervical vertebre. 
After a short course it joins the sixth nerve. From this union a broad nervous cord is 
derived, which proceeds to the shoulder, dividing into several branchlets, which supply 
the inner surface of the supraspinatus, &c. The sixth nervous trunk comes from the 
intervertebral foramen, between the fourth and fifth cervicals. It is a thick, flat cord, 
compared with the others, and joins, as aforesaid, the preceding fifth nerve. 
The seventh nerve, a large cord at first, is situated between the fifth and the sixth 
cervical vertebra, and has the vertebral artery lying above it. 
Lastly, the eighth cervical nerve, counting from before backwards, has exit from the 
foramen immediately above the first rib and between what appears to constitute the 
sixth cervical vertebra and the first dorsal. The two nerves, seventh and eighth, con- 
tinue outwards parallel to each other, deeper than but immediately anterior to the 
arch of the axillary artery. A twig from the chest or costal nerve joins the last on 
the scalenus muscle above the rib. 
The phrenic nerve, as already intimated, does not come either from the third or 
fourth branch of the cervical plexus, but instead appears to be the continuation of 
the bridge of junction betwixt the fifth and sixth. It leaves the latter with an outward 
flexure, being fastened by a loop of the cervico-axillary fascia over the artery, which may 
represent a thyroid axis. The nerve proceeds towards the chest, and enters it over the 
first rib, close to where the axillary artery is derived. What I presume to be the long 
thoracic is derived from the seventh and eighth nerves, and traverses the chest super- 
ficially to the enlarged lymphatics of the axilla, encompassed at first by the rete 
mirabile and further on lying upon the surface of the mammary gland. 
The dense mass of vessels matted to the brachial nerves prevented the composition of 
the primary cords being efficiently noted; but some of their tracks lower down were 
easier to follow. The median nerve, of moderate thickness, goes below the pronator 
radii teres, then on the flexor primi internodii pollicis, &c. to the wrist, underlying the 
flexor communis. Distally it splits into three branches, with subdivisions to the digits. 
The anterior interosseal division keeps company to beyond the pronator, thence, lying 
on the interosseous ligament, proceeds to the wrist and splits into twigs. A branch, 
apparently from the median, leaves it above the elbow-joint, runs to the brachialis 
anticus and distributes other twigs to the cubital joint and neighbouring parts. The 
musculo-spiral, a large thick cord, before reaching the humerus, splits into funiculi, 
part of which enter the triceps, brachialis anticus, &c. The radial nerve passes along- 
side the latter muscle, then beneath the pronator, and along the radius to the root of 
2E2 
