Herrick, Commissura hifirna. 415 



vestige which can, however, be followed more than five milli- 

 meters back into the spinal cord (fig. 10). This area corresponds 

 to the descending tract from the visceral commissural nucleus 

 described above for the gold fish. 



The somatic sensory centers of both the oblongata and spinal 

 cord are greatly enlarged, as well as elongated. The tuberculum 

 acusticum is large and extends far caudad over the vagal lobes. 

 From its lower end a somatic sensory field (fig. 6) extends back 

 laterally of the vagal lobe to connect with the lateral funicular 

 nucleus, which is well developed about as in Ameiurus. The 

 somatic commissura infima begins close behind the vagal lobes, 

 over-arching the visceral commissure and its nucleus (fig. 6). 

 This part of the somatic commissure contains a strong tract of 

 medullated fibers which pass from the caudal end of the tuber- 

 culum acusticum back through the lateral sensory field just referred 

 to, crossing as the most cephalic fibers of the somatic commissure 

 and terminating in the lateral funicular nucleus of the opposite 

 side (fig. 6, com. tub. acust). I have not observed such a tract 

 in any other fish which I have studied. Even in Gadus, which 

 also has very large tubercula acustica, there is no field of gray 

 matter extending between the tuberculum acusticum and the lat- 

 eral funicular nucleus and no tract can be distinguished in this 

 region for the commissura infima, though such a tract may pass 

 from the tuberculum acusticum indistinguishably mingled with 

 the others in the dorso-lateral fasciculus. In Gadus the tubercula 

 acustica fuse dorsally over the ventricle and there is a strong med- 

 ullated acoustic commissure in this area of fusion (see Kappers 

 igo6, figs, xcv to xcix). In Conger there is also a broad dorsal 

 fusion of the tubercula acustica but no medullated fibers appear in 

 it; nor is there an acoustic commissure of unmedullated fibers 

 except at the extreme cephalic end. It may therefore be that the 

 descending medullated tract for the commissura infima in Conger 

 is a compensation for the absence of an acoustic commissure in 

 the tubercula acustica themselves. But we should have more 

 precise knowledge of the courses of these fibers before accepting 

 this suggestion. 



The somatic commissura infima is larger than in any other fish 

 which I have examined except Prionotus. Its cephalic part is 

 large and very compact and lies dorsally of the visceral nucleus 

 and commissure (figs. 6, 7, 8). Its commissural nucleus is not 



