106 ANTHROPOLOGY. 
may be divided into secondary bundles composed of the ultimate or primit 
tive fibres. The composition of these has been already referred to. They 
present the appearance of a series of transparent tubes es in — 
juxtaposition without any intercommunication. | | 
The main trunk of a nerve breaks up into its component pinaies as 
it passes from centre to periphery, yielding up branches to the various parts 
it is destined to connect with the nervous centre. These branches gene- 
rally come off at acute angles, and soon plunge into the muscles and other 
parts to which they tend, dividing and subdividing as they proceed: An 
exception to this mode of branching is where a branch separates from the 
parent trunk at an acute angle, and then turns to run in an opposite direc- 
tion, forming an arch, from the convexity of which several branches are 
given off; such a nerve is said to be recurrent. 
In hese branchings, nerves subdivide, not only to pass immediately to 
their muscles or other distant parts, but also to connect themselves by cer- 
tain of these filaments with other nerves, and to follow the course of the 
latter, instead of adhering completely to that of the parent trunk. By these 
means nervous filaments, connected with very different parts of the brain 
and spinal cord, become bound together in the same fasciculus, and a nerve 
is formed, compounded of tubes possessing very opposite functions. The 
anastomosis of nerves formed in this manner differs essentially from the anas- 
tomosis of blood-vessels, in there being not the slightest communication of © 
the contents of the nervous tubes, as there is in the vascular. 
The plexuses are nervous anastomoses of the most complicated and 
extensive kind. Those which are connected with the spinal nerves are 
found in the neck, the axille, the loins, and the sacral regions. ‘There are 
also plexuses connected with the fifth nerve, the portio dura of the seventh, 
the glosso-pharyngeal, and the par vagum. Hach plexus is formed by the 
breaking up of a certain number of nervous trunks, the subdivisions of 
which unite to form secondary nerves, and these again, by further inter- 
change of fibres, give rise to nerves which emerge from the plexus, and 
consequently in their construction may derive their fibres from several of 
the trunks that enter the plexus. 
The object of the anastomosis of nerves appears to be to associate 
together nervous fibres connected with different parts of the brain or spinal 
cord. In this manner, nerve-tubes of different properties or endowments 
become united together in one sheath, forming compound nerves; and cer- 
tain sets of muscles, instead of receiving their nerves from a very limited 
portion of the cerebro-spinal centre, are supplied from a considerable extent 
of that centre, and each muscle may probably receive nerves which arise in 
different and distant parts of the spinal cord or brain; an arrangement 
whereby remote parts of those centres may be brought into connexion with 
neighboring muscles or other parts, or even with a single muscle. 
The nerves serve to conduct impressions from the external world to the 
nervous centres, or to transmit volitions from these centres to the structure 
at large, and especially to the muscular system. The former are called 
afferent or sensory nerves, the latter efferent or motor, and the two are 
812 
