?2 NORMAL HISTOLOGY. 



example, the median or the mandibular nerve, include three sets of nerve 

 fibres- (i) the efferent axones of the motor neurones, whose cell-bodies are 

 situated within the spinal cord or the brain-stem ; (2) the afferent dendntes 

 of sensory neurones within the spinal and other sensory ganglia; and (3) the 

 efferent axones of neurones within the sympathetic ganglia that accompany 

 the spinal fibres to the periphery for the innervation of the involuntary mus- 

 cle of the blood-vessels and of the skin and the glands. 



The nerve-fibres, the representatives of the three sets usually more or less 

 intermingled, are grouped into bundles, the funiculi, which differ in num- 

 ber and diameter according to the size of. the entire trunk that they form. 

 Each funiculus is surrounded by a definite sheath of dense connective tissue, 



Epineurium 



Blood-vessels 



Perineurium 



FiO. 97- Transverse section of small nerve-trunk composed of loosely united funiculi. X 20. 



the perineurium, which is continuous with the delicate fibro-elastic tissue pro- 

 longed as the endoneurium between the individual nerve-fibres. Where well 

 developed, the sheath of the funiculus consists of concentric fibrous lamellae, 

 which enclose the perineural lymph-spaces. The latter are in relation with the 

 lymph-clefts between the nerve-fibres, on the one hand, and with the lymphatics 

 within the interfunicular tissue on the other. When, as usually is the case, the 

 nerve is made up of several funiculi, these are loosely bound together and the 

 entire nerve-trunk so formed is invested by a general connective tissue envelope, 

 the epineurium, in which lie the larger blood-vessels and the lymphatics. 

 These coverings of the nerve-trunk are continued over its branches, even 

 over its smallest subdivisions. The last representative of these envelopes is 

 prolonged over the individual nerve-fibres as the sheath of Henle, which lies 

 outside the neurilemma and consists of flattened cells and delicate strands of 

 connective tissue. 



In cross-sections of the nerve-trunk (Fig. 98), the transversely cut indi- 

 vidual medullated nerve-fibres appear as small circles, sharply defined by a 

 fine outline (the neurilemma), each enclosing a deeply stained dot (the axis- 

 cylinder in section) ; the interval between the latter and the neurilemma cor- 

 responds to the space occupied by the myelin and usually appears clear and 

 unstained, with the exception of delicate and uncertain suggestions of mem- 

 branous septa. In contrast with the foregoing appearance, is that seen after 



