ELASMOBRANCH BRAIN ORGANIZATION 161 



processes. These dendrites may run directly toward the surface of the crest 

 or pass obliquely, crossing much of the crest (Paul and Roberts 1977a). The 

 unmyelinated fibers that make up most of the crest run rostrocaudally, 

 passing among the dendrites of the more deeply located cells in a topo- 

 graphical relationship similar to the passing of parallel fibers through the 

 Purkinje cells of the cerebellum. 



Alnaes (1973) argued that the crest fibers are primary lateralis afferents, 

 but Paul and Roberts (19776, 1977c) have demonstrated that lateral-line 

 input in Scyliorhinus does not directly activate the parallel fibers of the 

 crest. Boord and Campbell (1977) have shown that the lateral-line nerves 

 terminate in the nuclei deep to the crest, and in the auricle of the cerebellum, 

 but not in the crest itself. In Raja the cerebellar crest of the anterior lateral- 

 line lobe is crowned by a cap of granule cells termed the lateral granular 

 layer (lg, Figures 16, 22). This layer consists mainly of small granule cells, 

 among which are scattered a few much larger cells. The large cells are similar 

 to the Golgi cells located in the cerebellar granular layer. The lateral granular 

 layer not only caps the anterior lobe but also expands rostrally to cap the 

 posterior lobe as well (Figures 22D, 23). A similar condition exists also in 

 sharks (g, Figure 26), but here the granular layer is not visible laterally. It 

 continues rostrally over the lateral line lobes as they run under the upper leaf 

 of the auricle (ul, Figure 26). Following lesions of the lateral granular layer 

 in Raja, degenerating axons are seen leaving the granular layer and coursing 

 in the cerebellar crest, where they terminate on the dendrites of the deeper 

 Purkinje-like cells of the lobe (R. L. Boord, personal communication.) 



The bulk of the anterior and posterior lateral-line lobes consists of nuclei 

 containing several cell types. Large bipolar and triangular cells on the ventral 

 border of the crest send their superficial dendrites into the crest. Their deep 

 dendrites extend across the neuropil of the deep nucleus. Within this 

 nucleus, large, spherical neurons with widely branching dendrites and small, 

 densely staining cells predominate. The core of the anterior lateral-line lobe 

 receives electroreceptive afferents via the dorsal root of the anterior lateral- 

 line nerve, and it is termed the dorsal nucleus of the anterior lateral line lobe 

 (dn, Figures 21D, 22D). 



Lesions of the anterior lateral line lobe in Raja (R. L. Boord, personal 

 communication) reveal that its efferents first collect on the ventromedial 

 edge of the lobe, then run ventrally and medially to where the bulk of the 

 fibers cross the midline and enter the contralateral lateral lemniscus (11, 

 Figures 20, 23). Degenerating secondary lateralis fibers are traced rostrally in 

 the lateral lemniscus; they terminate in the nucleus of the lateral lemniscus 

 (nil, Figure 20 A) and in the mesencephalic lateralis nucleus (mln, Figure 

 20D). To my knowledge, the mesencephalic lateralis nucleus has not been 

 described in the literature before. Its projections and its homolog in sharks 

 are unknown. 



The organization of the posterior lateral-line lobe is more complex, as it 

 receives projections from both lateralis nerves and is closely associated with 

 the statoacoustic nuclei. The ventral root of the anterior lateral-line nerve 



