CENTRAL RELATIONS OF COMPONENTS. 55 



lins, which in higher animals contains the lateral cornu, 

 Clarke's column and other structures now commonly asso- 

 ciated with visceral nerves. The cells of the ventral 

 cornu lie farther ventrally. At the level of the paracen- 

 tral nucleus, but much farther laterally there runs through 

 the spinal cord another ill-defined area of "ground sub- 

 stance " containing few medullated fibres and occasional 

 very small cells (Fig. i6, /). This area, like the ventral 

 cornu, is more or less obscurely connected by strands 

 of non-niedullated (mainly spongiplasmic) fibres with 

 the other grey matter of the spinal cord. There is no 

 connecting bridge of cells in the case of the lateral 

 area. 



In the striped mullet, Mugil cephalus L,, which is 

 closely related to Menidia and a young specimen of which 

 (3 cm. long) was cut for comparison, we find the rela- 

 tions of the lobus vagi and its fibre connections very 

 much as above described, with, however, the spinal 

 portion more highly developed and more clearly differ- 

 entiated. The caudal ends of the lobi vagi contract 

 toward the ventricle and are continued into the spinal 

 cord without an appreciable break. They finally lie 

 closely appressed between the dorsal cornua and the ven- 

 tricle and now numerous medullated fibres appear in 

 them, a part or all of which cross dorsally of the canalis 

 centralis after the fourth ventricle has closed, thus enter- 

 ing the commissura infima. A small bundle of medullated 

 fibres is continued caudad of the commissure to about the 

 level of the first spinal nerve. Its fibres gradually disap- 

 pear, leaving the bundle in different directions, chiefly 

 laterally and ventrally. 



The motor nucleus of the IX and X (nucleus ambiguus) 

 is very large and its cells are arranged in the characteristic 

 dense rosettes. It extends far caudad beyond the end of 

 the lobus vagi, maintaining the same position, /. e., lat- 

 erally and dorsally of the canalis centralis, until the level 

 of the first spinal nerve. Here it ends abruptly, as in 

 Menidia. In the mullet the ventral cornu cells extend 

 cephalad considerably farther than the terminus of this 



