EXTERNAL FORM. 



Fig. 344. — Antekior and Posteuioii Views op 

 THE JIedulla Oblongata and Spinal Cord 

 WITH Sections (Allen Thomson), i 



The cord has been divested of its membranes 

 and the roots of the nerves. A presents au 

 anterior, B a jMsterior view, showing the upper 

 ceiwical), and the lower (lumbar) enlargements. 

 In these figures the filiform prolongation, repre- 

 sented separately in B', has been removed ; C 

 shows a transverse section through the middle of 

 the medulla oblongata ; D, a section through tlie 

 middle of the cervical enlargement of the spinal 

 cord ; E, through the upper region of the dorsal 

 part ; F, through its lower ; (j, through the middle 

 of the lumbar enlargement ; and H, near the lower 

 end of its tapering extremity. 



1, anterior pyramids ; 1', their decussation ; 

 2, olivary bodies ; 3, restiform bodies ; 4, pos- 

 terior surface of the medulla oblongata ; 4', cala- 

 mus scriptorius ; 5, posterior pyramids ; 6, pos- 

 terior lateral columns passing up into the restiform 

 bodies ; 7, 7, anterior median fissure extending 

 througli the whole length of the spinal cord ; 8, 8, 

 anterior lateral groove ; 9, 9, posterior median 

 fissure ; 10, 10, posterior lateral groove ; x , 

 lower end of the tapering extremity of the cord ; 

 X , X , in B', the filiform prolongation of the 

 cord and its pia-matral covering. 



Size and extent. — The length of the 

 Sjiiual cord is from fifteen to eighteen 

 inches. • In general form it is cylindrical, 

 somewhat flattened before and behind. 

 It presents two enlargements — an upper 

 or cervical, .and a lower or lumbar (fig, 

 344, D and G). The cervical enlarge- 

 ment is of greater size and extent than 

 the lower. It reaches from the third 

 cervical to the first dorsal vertebra ; its 

 greatest diameter is from side to side. 

 The lower or lumbar enlargement is 

 situated nearly opposite the last dorsal 

 vertebra ; its antero-posterior diameter 

 is nearly equal to the transverse. Below 

 this enlargement, the cord tapers in the 

 form of a cone {conns 7nedidhris), from 

 the apex of which the small filiform 

 prolongation is continued downwards 

 for some distance wdthin the sheath. 



Fig. 344. ^ 



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 development in the embiyo. the spinal 

 cord is destitute of these enlargements, which, 

 in their first appearance and subsequent pro- 

 gress, correspond with the growth of the 

 limbs. 



?-! 



