EXTERNAL FORM. 



medulla oblongata ; D, a section through the middle of the 

 cervical enlargement of the cord ; E, through the upper 

 dorsal region ; F, through the lower dorsal region ; G, through 

 the middle of the lumbar enlargement ; and H, near the lower 

 end of the conus medullaris. 



1 to 6 refer to parts of the medulla oblongata ; the 

 remaining numbers to parts of the spinal cord. 



1, pyramids ; 1', their decussation ; 2, olivary bodies ; 

 3, lateral columns ; 4, fourth ventricle ; 4', calamus scrip- 

 torius ; 5, funiculus gracilis ; 6, funiculus cuneatus ; 7, 

 7, anterior median fissure of the spinal cord ; 8, 8, postero- 

 lateral groove corresponding to the attachments of the pos- 

 terior nerve-roots ; 9, 9, posterior median fissure ; x , taper- 

 ing extremity of the cord ; x , x , in B', filum terminale. 



cord is not, however, of uniform diameter 

 throughout, but is swollen out in the cervical 

 and lower dorsal regions, two enlargements 

 being thereby produced an upper or cervical 

 (brachial), and a lower or lumbar (crural) (fig. 4). 

 Of these the cervical enlargement is of greater 

 size and extent than the lumbar. It extends from 

 the upper limit of the cord to the body of the first 

 or second thoracic vertebra ; it is largest oppo- 

 site the fifth or sixth cervical vertebra, where it 

 measures from 13 to 14 mm. from side to side. 

 The lower or lumbar enlargement begins at the 

 tenth thoracic vertebra, is largest opposite the 

 twelfth (11 13 mm. across), and from this 

 point becomes gradually smaller ; its antero-pos- 

 terior diameter is more nearly equal to the 



Fig. 5. DIAGRAMMATIC VIEW FROM BEFORE OF THE SPINAL 



CORD AND MEDULLA OBLONGATA, INCLUDING THE ROOTS 

 OF THE SPINAL AND SOME OF THE CRANIAL NERVES, AND 

 ON ONE SIDE, THE GANGLIATED CHAIN OF THE SYMPA- 

 THETIC. (Allen Thomson.) {. 



The spinal nerves are enumerated in order on the right 

 side of the figure. Br, brachial plexus ; Cr, anterior 

 crural, 0, obturator, and Sc, great sciatic nerves, coming 

 off from lumbo-sacral plexus ; x , x , filum terminale. 



a, 6, c, superior, middle and inferior cervical ganglia of 

 the sympathetic, the last united with the first thoracic, 

 d ; d', the eleventh thoracic ganglion ; I, the twelfth 

 thoracic (or first lumbar) ; below s s, the chain of sacral 

 ganglia. 



transverse than is the case in the cervical en- 

 largement. Below the lumbar enlargement the 

 cord tapers in the form of a cone (conus medul- 

 laris'), from the apex of which the small fili- 

 form prolongation is continued downwards. 



The cervical and lumbar enlargements have 

 an evident relation to the large size of the 

 nerves which supply the upper and lower limbs, 

 and which are connected with those regions of 

 the cord. At the commencement of its develop- 

 ment in the embryo the spinal cord is destitute 



of these enlargements, which, in their first appearance and subsequent progress, 

 correspond with the growth of the limbs. 



The terminal filament (filum terminale, central ligament) (fig. 6, 5, V) descends 



