HISTOLOGY OF THE NERVOUS SYSTEM. 



95 



2. Fibrous Portion. This occupies the central part. It 

 consists of a close and complicated network of nerve-fibres inter- 

 mingled with connective tissue. Some of these fibres communi- 

 cate with branches of the nerve-cells, as stated above ; others 

 run out into the lateral nerves, while still others run along the 

 commissures to connect with fibres from other ganglia. 



Fio. 42. Two of the ventral ganglia (I, II) of Lumbricus with the lateral nerves, 

 showing some of the motor nerve-cells and fibres (black), a sends fibres for- 

 wards and backwards within the nerve-cord ; fr, a fibre into one of the double- 

 nerves on its own side ; c and d, fibres that cross to the nerves of the opposite side. 

 (After Retzius.) 



According to the latest researches (of Lenhossek and Retzius) most if 

 not all of the nerve-cells of the ventral cord are motor in function. Near 

 the centre of each ganglion (Fig. 42, e) in a single large multipolar cell of 

 doubtful nature. All the other cells are either bipolar or unipolar, in the- 

 latter case sending out a single branch which soon divides into two. In 

 every case one of the branches breaks up into fine sub-divisions within the 

 cord. The other branch in most cases passes out of the cord through one 

 of the lateral nerves to the muscles or other peripheral organs, either 



