290 



THE ANIMAL PARASITES OF MAN 



L.n. 



Lf. 





1 





the neck and the entire series of proglottids. Within the proglottids 

 it consists of a number of longitudinal nerve fibres of which those at 

 each lateral border are usually the largest. In the Taeniae the lateral 



nerves are accompanied both 

 dorsally and ventrally by a 

 thinner nerve (accessory nerve) 

 (fig. 185) ; on each surface, 

 moreover, between the lateral 

 nerve and the median plane, 

 there are two somewhat 

 stronger bundles (sub-median), 

 so that there is a total of ten 

 longitudinal nerve bundles. 

 They lie externally to the trans- 

 verse muscle plates, and the 

 lateral and accessory bundles 

 lie externally to the principal 

 excretory vessels, and are every- 

 where connected by numerous 

 anastomoses and secondary 

 anastomoses ; one typical ring 

 commissure is usually found 

 at the posterior border of the 

 segments. [.In the Bothrio- 

 cephalida the distribution of 

 the nerve bundles is different 

 (for instance, two lie in the 

 medullary layer), or they are 

 split up into a larger number 

 of branches. In the scolex the nerve bundles are connected in a very 

 remarkable manner by commissures with that which is generally 

 termed the central part of the entire nervous system. There occurs 

 normally a commissure between the two lateral nerves ; at the same 

 level, the dorsal and ventral median nerves are also connected at each 

 surface as well with each other^as with the lateral nerves, so that a 

 hexagonal or octagonal figure is formed. The so-called apical nerves 

 pass from this commissural system anteriorly, embrace the secondary 

 muscular system of the rostellum semicircularly, and form an annular 

 commissure (rostellar ring) at the inner part of the rostellum. 



The peripheral nerves arise from the nerve bundles as well as 

 from the commissures situated in the scolex ; some go direct to the 

 muscles, while others form a close plexus of nerves external to the 

 inner longitudinal muscles, which plexus likewise sends out fibres to 

 the muscles, but principally to [[numerous fusiform sense organs 



FIG. 187. Longitudinal section of the head 

 and neck of Tania crassicollis, showing the 

 lens-shaped muscular rostellum, with two hooks 

 lying in the concentric cup-like mass of muscles. 

 L.m., longitudinal muscles of the neck ; Z/"., left 

 lateral nerve ; 6*., ganglion ; S.c., subcuticular 

 layer ; W^ external, W*, internal excretory 

 vessel. 0/1. 



