12 Howard Avers and Julia AA^orthington 



The Lateralis Nerves. 



The lateralis system is but slightly developed in Bdellostonia when 

 compared with its condition as found in higher fishes and the Amphibia. 

 Its peripheral nerves are distributed exclusively to the head, but both 

 anterior and posterior lateralis nerves are represented, and tl:e sense 

 organ canals and isolated lateral line organs, neuromasts, are also 

 present. The N. lateralis posterior leaves the brain as a distinct cranial 

 nerve, while the fibers of the lateralis anterior are bound up with and 

 accompany both trunks of the trigeminus. There are indications that 

 a few of them may -also accompany the facialis. 



There are two groups of lateral line canals in the head of Bdellostonia, 

 an anterior group, innervated by the lateralis anterior, and a posterior 

 group, innervated by the lateralis posterior. The anterior group is 

 composed of four, occasionally three, or five short canals, nearly equi- 

 distant from each other, and located on the side of the head in front of 

 the eye of its side of the body (Fig. 48). The posterior group lie? on 

 the dorsal surface of the head and consists of two divisions ; the three 

 (occasionally two) inner canals run meso-laterad, and the outer ones run 

 at a slight angle to the long axis of the body (Fig. 49). These canals 

 are almost impossible to find in the full grown adult, but in young 

 hagfish, about eleven inches long, they are easily seen on heads that 

 have been hardened in chromic acid. A description of their structure 

 and of the effect of different hardening agents upon the underlying 

 tissue has already been given in a previous paper (Ayers and Worth- 

 ington, '07). 



The lateralis components in the nerves of Bdellostonia, owing prob- 

 ably to their inferior bulk and the intimate association of the anterior 

 fibers with those of other systems, have been overlooked by most of the 

 previous workers in Myxinoid anatomy, not only by tho^e who were 

 working principally by dissection and dealing with the entire head, but 

 also by those who were working with sections and making a special 

 study of the brain. Sanders, '94, makes no mention of them whatever, 

 not having detected their presence even in the second trigeminus trunk, 

 and apparently not having seen that part of the lateralis posterior that 

 lies between the cranial capsule and the brain. He seems to have 

 included a description of the peripheral part of the lateralis posterior 

 in his "upper division of the trigeminus/' but his account of the dis- 

 tribution is so brief and vague that it is difficult to tell what he reallv 



