DE. J. MUEIE ON THE FOEM AND STEUCTUEE OF THE MANATEE. 185 



the first, has its exit from the same foramen as the third — namely, betwixt the second 

 and third cervical vertebi-se ; 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 fiftli is of considerable calibre, and 

 issues between the scalene tendons, marking the thii-d and fourth cervical vertebrae. 

 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 vertebrae, 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 Hgament, 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 



