340 H. W. NORRIS AND SALLY P. HUGHES 



section through the dorsal root at its point of entrance into the 

 brain shows that its fibers pass into the brain substance on each 

 side of a vertical internal furrow or sulcus in the lateral-line 

 lobe (fig. 39), in this way spreading fan-shape in the brain wall. 

 In a similar fashion the ventral root fibers spread anteriorly and 

 posteriorly in the acusticum (figs. 25 to 30). According to 

 Strong ('03), the dorsal root is formed by the union of fibers 

 from the truncus hyomandibularis and ramus buccalis, but the 

 ventral root fibers are derived from the ramus ophthalmicus 

 superficialis VII and pass through the dorsal root in order to 

 reach the acusticum. Cole ('96) and Cole and Dakin ('06) state 

 that in Chimaera the rami ophthalmicus superficialis, buccalis 

 and hyomandibularis each connects with the brain by a dorsal 

 [lateral-line lobe] and a lateral [acusticum] root. Allis ('01) states 

 that in Mustelus the dorsal (superficial ophthalmic) and ventral 

 (buccal-hyomandibular) roots of the 'trigeminus II' [lateral-line 

 conponent of the facialis] each connects with the ' lobus trigemini' 

 [lateral-line lobe] and with the tuberculum acusticum. This 

 account of Allis the writers corroborate, but would add that in 

 Mustelus both the hyomandibularis and the buccalis send fibers 

 into the lateral-line lobe and also into the acusticum. In brief, 

 the relations in Mustelus are exactly like those in Chimaera. 

 It seems highly improbable that the conditions in other elasmo- 

 branchs are different from those in Mustelus and Chimaera. 

 In Squalus the interweaving of the root fibers makes it well nigh 

 impossible to determine with accuracy their peripheral distribu- 

 tion, although from a study of Squalus material alone the writers 

 would agree with Strong. As Cole and Dakin state for Chimaera, 

 so for Mustelus it may be said that the truncus hyomandibularis 

 sends but few fibers into the acusticum. 



Hawkes ('06) states that in Chlamydoselachus the hyo- 

 mandibular trunk arises from the brain at the same level as the 

 root of ilic trigeminus and facialis proper, and that the super- 

 ficial ophthalmic \ll and buccal arise by two roots situated 

 more dors; illy. It seems to the writers more probable that the 

 so-called hyomandibular roots in ( 1 hlamydoselachus are the vis- 

 ceral sensory and motor, and that the 'rami communicantes' 



