546 



STRUCTURE OF VERTEBRATA 



motor fibres (correlated with the great development of visceral 

 musculature in the head). 



P.' PI 



Fig. 308. — Diagrammatic section of spinal cord. 



p.j.. Posterior fissure ; p.c, posterior column of white matter ; 

 d.p.s., dorsal, posterior, sensory or afferent root ; g., ganglion ; 

 v.a.m., ventral, anterior, motor or efferent root ; c.n., com- 

 pound spinal nerve with branches ; s.g., sympathetic ganglion ; 

 a.c, anterior column — the anterior iissure is exaggerated ; 

 g.c, ganglion cells ; g.m., grey matter ; zv.m., white matter. 



Fig. 309. — Diagram of spinal cord of man, thoracic 

 region. — After Johnston. 



S.S., Somatic sensory ; V.S., visceral sensory ; S.M., somatic motor ; V.M. 

 and U.M., visceral motor ; d.r., dorsal root ; U.R., ventral root. 



(3) The pre-mandibular primitive segment (I.) was probably supplied 

 by the oculomotor (ventral) and the ophthalmicus profundus (dorsal). 



The mandibular primitive segment (II.) was probably supplied by 

 the pathetic (ventral) and the trigeminal (dorsal), 



