'36 



SE LA CHI I 



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

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



civ 



Fr.. 93. 



Inner view of the right half >it the skull of Hexunchns. (After Gegenbaur. I uc, foramen for 

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

 tg, for trigeminal, tr, for trochlear, vg, for vagus, and ys, for occipito-spinal nerve ; cup, 

 nntorbital process : c, carotid foramen : ca, interorbital canal ; in, 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. it 



Lanina cot nubica, Gm. A. portion of the vertebral column of the trunk, partly cut longi- 

 tudinally (right-side view). 1!. transverse section of the same through the middle ol acentrum. 

 c, centrum : ca, calcareous constricted ring ; d.r, foramen for dorsal nerve-root ; /<». basi\ entral : 

 in, interdorsal ; iv, interventral : li, ligament : na, basidorsal : n.c, neural canal ; ;.', notochord ; 

 r.ca, radial calcifications; v.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 



