MODES OF TERMINATION OF NERVE-FIBRES. 101 



afterwards studied. End-bulbs are found in the conjunctiva of 

 the eye, where in most animals they have a cylindrical or oblong 

 shape (fig. 117), but in man are spheroidal (fig. 118). They have 

 also been found in papillae of the lips and tongue, and in the 

 epineurium of the nerve-trunks, and somewhat similar sensory end-_ 

 organs also occur in the integument of the external genital organs of 

 both sexes (figs. 116, 121). Similar 

 bodies of larger size are also met 

 with in the neighbourhood of the 

 joints (fig. 120). In the skin 

 covering the bills of certain birds 

 {e.g. duck), a simple form of end- 

 organ occurs, consisting of two or 

 more cells arranged in rows within a FIG. 122. TACTILE CORPUSCLES FROM THE 

 capsule, with the axis-cylinder ter- DUCK'S TONGUE. (Izquierdo.) 



f, . A, composed of three cells, with two inter- 



minatmg in flattened expansions posed disks, into which the axis-cylinder of 



i . ,i_ IT / 7 x the nerve, w, is observed to pass ; in B there 



between the Cells (COrpUSCleS OJ i s but one tactile disk inclosed between two 



Grandry, fig. 122). 



The Pacinian corpuscles are larger, and have a more complex 

 structure, than the tactile corpuscles and end-bulbs (fig. 123). They 

 .are composed of a number of concentric coats arranged like the layers 

 of an onion, and inclosing the prolonged end of a. nerve-fibre. A single 

 medullated nerve-fibre goes to each Pacinian corpuscle encircled by 

 -a prolongation of perineurium, and within this by endoneurium ; when 

 it reaches the corpuscle, of which it appears to form the stalk, the 

 lamellae of the perineurium expand to form some of the tunics of the 

 corpuscle. The nerve passes on, piercing the other tunics, and still 

 provided with medullary sheath, and surrounded by endoneurium, to 

 reach the centre of the corpuscle. Here the endoneurium is prolonged 

 to form a sort of core of cylindrical shape, along the middle of which 

 the nerve-fibre, now deprived of its medullary and primitive sheaths, 

 passes in a straight course as a simple axis-cylinder (figs. 123, ri ; 124, 

 './. ) to terminate at the farther end of the core, either in an arborisation 

 or in a bulbous enlargement. 



The tunics of the corpuscle are composed of connective tissue, the 

 fibres of which for the most part run circularly. They are covered on 

 both surfaces with a layer of flattened endothelial-cells, and here and 

 there cleft-like lymph-spaces can be seen between them like those 

 between the layers of the perineurium (see p. 88). 



When sensory nerve-fibres terminate in plexuses, they generally 

 branch once or twice on nearing their termination. , The sheaths of the 

 fibres then successively become lost, first the connective tissue or peri- 



