324 



CONSTRUCTION OF THE NERVES AND NERVE-ROOTS. 



brain and cord) which here and there dip in from the surface either as septa, such 

 as that which passes into the posterior fissure of the spinal cord, or as carriers of 

 blood-vessels, which everywhere enter the substance of the centro-spinal centre 

 from the vessels of the pia mater. 



CONSTRUCTION OF THE NERVES AND NERVE-ROOTS. 



The nerves are formed of the nerve-fibres already described, collected together 

 and bound up in sheaths of connective tissue. A variable number of fibres inclosed 

 in a tubular sheath forms a slender round cord of no determinate size, usually 

 named a funiculus ; if a nerve is small it may consist of but one such cord, but in 

 larger nerves several funiculi are united together into one or more bundles, which, 

 being wrapped up in a common membranous covering, constitute the nerve (fig. 379). 

 Accordingly, in dissecting a nerve, we first come to an outward covering, formed of 

 connective tissue, often so strong and dense that it might well be called fibrous. 

 From this common sheath we trace connective tissue bundles passing between the 

 funiculi, connecting them together as well as conducting and supporting the fine 



Fig. 379. SECTION OF THE INTERNAL SAPHENOUS NERVE (HUMAN), MADE AFTER BEING STAINED IN 



OSMIC ACID AND SUBSEQUENTLY HARDENED IN ALCOHOL. DRAWN AS SEEN UNDER A VERY LOW 

 MAGNIFYING POWER. (E. A. S.) 



ep, epineurium, or general sheath of the nerve, consisting of connective tissue bundles of variable 

 size, separated by cleft-like areolse, which appear as a network of clear lines, with here and there fat- 

 cells / /, and blood-vessels v : per, funiculus enclosed in its lamellated connective tissue sheath 

 (perineurium) ; end, interior of funiculus, showing the cut ends of the medullated nerve-fibres, which 

 are embedded in the connective tissue within the funiculus (endoneurium). The fat-cells and the nerve- 

 fibres are darkly stained by the osmic acid, but the connective tissue of the nerve is less stained. 



blood-vessels which are distributed to the nerve. But, besides the interposed areolar 

 tissue which connects these smallest cords, each funiculus has a special sheath of its 

 own, as will be immediately noticed. 



The common sheath (fig. 379, ep) and its sub-divisions consist of connective 

 tissue with the usual white and elastic constituent fibres of that texture, the latter 

 being present in considerable proportion : frequently also a little fat is to be found. 



