136 



SELACH1I 



from the outer layer (Raja). This outer layer is sometimes, at all 

 events, formed outside the elastica externa, by a spreading out of 



out 



vs. 



ecu 



Fir,. 03. 



Inner view of the right half of the skull of }Ie.va,nchus. (After Gegeubaur.) ac, foramen fo 

 auditory, gp, for glossopharyngeal, o, for optic, ocn, for spino-occipital, om, for oculomotor, 

 tg, for trigeminal, tr, for trochlear, vg, for vagus, and vs, for occipito-spinal nerve ; a.j>, 

 antorbital process ; o, carotid foramen ; cot, interorbital canal ; m, membrane over fontanelle ; 

 r, rostrum. 



the bases of the arches, which finally meet round the notochordal 

 centrum. A compound centrum is thus formed, partly 'perichordal' 



nt dr, vr ' na w 



FIG. 94. 



Lamna corwtibica, Gin. A, portion of the vertebral column of the trunk, partly cut longi- 

 tudinally (right-side view). B, transverse section of the same through the middle of a centrum, 

 c, centrum ; en, calcareous constricted ring ; d.r, foramen for dorsal nerve-root ; ha, basiventral ; 

 in., interdorsal ; / c, interventral ; li, ligament ; na, basidorsal ; n.c, neural canal ; tit, notochord ; 

 r.ca, radial calcifications ; c.r, foramen for ventral root ; w, intervertebral ligament. 



and partly 'chordal' (p. 100). The ventral root of the spinal 

 nerves, as a rule, comes out either behind or through the neural 

 arch (basidorsal) ; the dorsal root either behind or through the 



