ELASMOBRANCH BRAIN ORGANIZATION 



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Figure 25 Lateral view of the brain stem of Mustelus canis showing the relationships of 

 the various branches of the anterior lateral-line nerve and its dorsal and ventral roots. The 

 superficial roots of Vth, Vllth, VHIth, and posterior lateral-line nerves are also shown. 

 ALL, anterior lateral-line lobe; Rbd, dorsal root of buccal ramus of anterior lateral-line 

 nerve; Rbv, ventral root of buccal ramus of anterior lateral-line nerve; RLLp, root of pos- 

 terior lateral-line nerve; Rmed, dorsal root of external mandibular ramus of anterior 

 lateral-line nerve; Rmev, ventral root of external mandibular ramus of anterior lateral-line 

 nerve; Rod, dorsal root of otic ramus of anterior lateral-line nerve; Rosd, dorsal root of 

 superficial ophthalmic ramus of anterior lateral-line nerve; Rosv, ventral root of super- 

 ficial ophthalmic ramus of anterior lateral-line nerve; Rov, ventral root of otic ramus of 

 anterior lateral-line nerve; RVm, root of mandibular ramus of V; RVos, op, mx, super- 

 ficial ophthalmic, deep ophthalmic and maxillary roots of V; RVIIvm, visceral motor root 

 of VII; RVIIvs, vsiceral sensory root of VII; RVIII, root of VIII. (After McCready and 

 Boord 1976.) 



The statoacoustic nerve consists of anterior and posterior rami (Figures 

 8, 9, 12, 13, 16, 17). The anterior ramus innervates the anterior and horizon- 

 tal semicircular canals and utricle, and the posterior ramus innervates the 

 posterior semicircular canal, saccule, and lagena (Popper and Fay 1977). As 

 the rami course toward the medulla, they fuse to form a single ganglion and 

 root, which enters the medulla together with the roots of the facial nerve. 

 Upon entering the medulla (Figure 22D), the statoacoustic fibers occupy a 

 ventral portion in the posterior lateral line lobe and form ascending and 

 descending tracts. 



