14 



G.J. HOWES 



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Fig. 2. Distribution of neuromasts types 1 and 2 in A, Melanonus zugmayeri on dorsal surface of head and B, M. gracilis on lateral surface 

 of head. C, innervation pattern of type 1 neuromasts in subnasal region (right side) of M. zugmayeri (dashed lines indicate nerves, arrow 

 heads indicate termination of nerve branch; large arrow points anteriorly). In this and subsequent figures, scale bars in millimetre divisions. 





oblique row across the lower part of the cheek and a double 

 row across the epioccipital region (Figs 2A,B). The neuro- 

 masts do not extend backwards on to the body. 



There are about 500 flange-like neuromasts covering the 

 entire head. Innervation is by the ramus canalis lateralis (Rcl 

 sensu Freihofer, 1970) which exits from the posterior frontal 

 foramen to anastomose through a loose fascia of connective 

 tissue. The neuromasts are innervated by subranches stem- 

 ming from a complex nerve network (Fig. 2C). 



The Rcl nerve branches from the supraorbital trunk of the 

 trigeminal complex, (Fig. 17), a condition similar to that in 

 Merluccius (Freihofer, 1970). The branch innervating the 

 large posterior neuromasts enclosed in the frontal sensory 

 canal detaches separately from the supraorbital trunk, 

 whereas in Merluccius the nerves separate off together. 



The large, plate-like neuromasts, housed in the sensory 

 canals number two in the nasal bone, three in the frontal (one 

 beneath the anterior medial ridge, one beneath the lateral 

 arch and one posteriorly), one in the anterior part of the 



pterotic, one in the parietal, one in each extrascapular, three 

 in the first infraorbital, one in the second, third and fourth, 

 two in the fifth and one in the sixth, and five in the 

 preoperculum. 



Infraorbitals (Fig. 3). 



There are six infraorbital bones, the first long and relatively 

 deep with a broadly fretted ventral border, the outer flange 

 which forms the roof to the sensory canal extends as a shelf 

 along the anterior half of the bone, but curves laterally along 

 the posterior half. The ascending process which contacts the 

 posterior wall of the lateral ethmoid is tall and spine-like. The 

 second infraorbital is confluent with the first and is as deep 

 but only a sixth of its length. The medial lamina of the third is 

 widely separated from that of the second although the 

 dorsolateral flange is nearly in contact. The third together 

 with the fourth form the posteroventral corner of the orbit 

 and the fourth has only a short orbital margin and flange 



