INTRODUCTORY. 13 



their whole length, performing the function of a ligament 

 in addition to their motorial value. Muscles are gene- 

 rally connected together by areolar tissue, in dissecting 

 them the knife should be always used in the direction of 

 their fibres, their attachments more particularly investi- 

 gated, but their relations and figure also taken into account. 

 Nerve-tissue next demands notice, as being the source of 

 all muscular action, sensation, and intellect. The nervous 

 system is primarily divided into the cerebro-spinal and 

 sympathetic systems, each of which consists of nerves and 

 nerve-centres ; the two are intimately blended. The cerebro- 

 spinal nervous system is that which regulates animal 

 life, i. e. sensation, voluntary motion, and intellect. Its 

 centres are the brainand spinal cord ; its nerves are marked 

 by whiteness, they are given off from the above-mentioned 

 centres, as a rule, in pairs, one from each side of the centre. 

 Those of the spinal cord originate hy two sets of fibres, a 

 superior or sensory, from the supero-lateral part of the cord ; 

 each of these has a ganglion upon it and subsequently 

 unites with the inferior or motor root. After this the sen- 

 sory cannot be distinguished in any way from the motor 

 fibres ; the difference lies not in the fibres, but in the parts 

 to and from which they run. The sympathetic, gang^lionic, 

 or vegetative system superintends those organs which 

 provide directly for the maintenance of the individual or 

 the perpetuation of the species. Its centra consist of a 

 number of grey nodular bodies, enlargements of the nerves, 

 found in various parts of the body (termed ganglia) . Thus, 

 they exist as a chain of ganglia connected together by 

 fibres on either side of the spine, as special ganglia existing 

 in certain organs as the heart, as the ganglia on the sensory 

 roots of the cerebro-spinal nerves, and as certain ganglia 

 situated in certain irregular but constant parts of the body, 

 as those of the fifth cranial nerve. From these fibres run, 

 collected into nerves distinguishable by their darker colour 

 than those of the animal system. These and the cerebro- 

 spinal nerves communicate in every possible manner. 

 Two classes of histological elements are distinguishable in 

 nerve-tissue, fibres and cells. The nerves are composed only 

 of fibres which are of two kinds, grey and white. The grey 

 fibres so much resemble unstriated muscular fibre that 

 their nervous nature has been doubted. They are found 

 most largely in the sympathetic nerves, of which they form 



