,ST,ST/-;.W 



7 .">."> 



with tlie fourth or posterior ventricle passes under (lie corpora o^iadrigcmina and is known aa 

 t, ie aqueduct of Sylvius, or amueductiu cercbn. 



'I'he locali-ed thickening of the uall of tin' neural canal results from the combined prolifer- 

 ai ion and migration of its component cells. These proliferating cells have been called germinal 



FIG. 501. DIAGRAMMATIC H<>I;I/I,M u. Si,. TMN in A VI:HTEHIIATE BRAIN. (After Huxley.) 



MI-:ri:\i -ICI-HA LO.V Til A I. A Ml .V 



LA TERA I. 



rjtlfTJUCLX 

 OLFACTORY 



nn 1:1:1 K'i'i. i .\i 



LA .VISA 



TERMIXALIS 



MEIX'I.LA 

 OBLONGA I. 



CEREBELLUM 



CORPUS 

 XTHIATVM 



MOXRO 



cells. The products of their division are apparently indifferent at first, but later they become 

 differentiated into two varieties: (1) Spongioblasts, or those cells which will develope into neu- 

 roglia, and (2) neuroblasts, or those cells which will develope into neurones. The neuroblasts 



FIG. 562. DIAGRAM SHOWING THE SEGMENTS AND THE FLEXURES OF THE HUMAN BRAIN AND THE 

 EXPANSION OF THE CEREBRAL HEMISPHERES OVER THE OTHEU PORTIONS OF THE BRAIN. 



EPIPHYSIS 



CORPORA Qr.t/)A'/'.-/;i//v i 



(mid-br.iin i 



(Itiml-lnnin) 

 FOURTH VENTRICLE 



CEREBRAL HEMISPHERE 

 CORPUS CALLOSI V 

 SK/'JI'M l'l:LU:CIHl M 

 FOSJfTJT 



FORA MEN OF MOKRO 

 THIRD VENTRICLE 

 HYPOPHYS1K 

 CEREBRAL PEDUNCLE 

 PONS | 



MEDULLA OBLONGATA^ 



SPINAL CORD 



>(hind-brain) 



become transformed into neurones of the sizes, shapes., and arrangements characteristic of the 

 localities in which the transformation occurs. 



Neurones whose cell-bodies belong to the peripheral nervous system are not developed within 

 the walls of the central system at all. They (comprising the spinal ganglion neurones and those 



FIG. 563. DIAGRAMS SHOWING (1) THE GROWTH OF THE PRIMITIVE GANGLIA FROM THE NEURAL 

 CHEST; -(2) THE DIVISION OF THE PRIMITIVE GANGLIA INTO SPINAL AND SYMPATHETIC 

 PORTIONS, AND (3) THE FORMATION OF THK NKRVES. 



KTODiBM 

 NlffXAl 



XKI-1UI. CRUST 

 (Ci.ayj.wrmo) 



SUSFACS SCTODSRX 



. TfHK 



a rvi'i TiiKTir nn xni. in v 



of Hie sympathetic system) are derived from the cells of the neural crest. The wedge-shaped 

 mass comprising (he neural crest, through the proliferation of its cells, gradually extends 

 outwards over the surface of the neural tube alon^ either side. Soon the proliferation becomes 



