THE SPLANCHNIC NERVES. 93 



proventriculus are the largest. They are all united with a 

 central ganglion, which I shall term the median ganglion. 



The median ganglion is situated on the dorsal surface of 

 the oesophagus, immediately behind the commissure of the 

 hemispheres. It is a pyramidal enlargement of the median 

 splanchnic nerve. It receives several nerve cords from the crura 

 of the hemispheres at its base, and gives off branches from its 

 apex which are attached to the posterior margin and external 

 surface of the ring ; they surround the dorsal vessel and supply 

 it, and terminate in the ganglion of the crop. 



The portion of the median nerve in front of the central 

 ganglion divides into several branches, which form a plexus 

 around the oesophagus. These end in the ganglion of the 

 pharyngeal sinus. 



The Ganglion of the Pharyngeal Sinus consists of a number of 

 large stellate nerve cells, the processes of which terminate in 

 the intrinsic muscles of the pharynx. Many of these cells 

 measure 2O M to 3O M in diameter ; they are not closely packed 

 together, but are scattered in the posterior part of the sinus 

 and lie chiefly close to the pharyngeal epithelium. Beside these 

 ganglion cells there is a considerable quantity of lymphoid 

 tissue and a group of cells similar to those which form the 

 pericardial septum in the sinus (Fig. 8, /). 



The posterior portion of the median nerve remains undivided 

 and terminates in the ganglion of the proventriculus (page 57). 

 This ganglion not only supplies the proventriculus and chyle 

 stomach, but gives off several ganglionated nerves on each side 

 to the salivary glands (page 61). 



Further details of structure and the manner in which the 

 ganglion cells are related to the parts they supply will be given 

 in the histological section of this work. 



APPENDIX TO CHAPTER IV. 



METHODS OF STUDY. 



THE great improvements of modern histological research are 

 the perfect fixing of the tissues, the use of a nuclear in the 



