784 



THE NERVOUS SYSTEM. 



3. Asymmetry of the cord with congenital defects of the extremities or muscles, 

 such as intra-uterine or other amputations, clubfoot, etc. 



4. Variations in the volume of the cord as a whole. 



FALSE HETEROTOPIA. Congenital displacement of the gray or white matter of the 

 spinal cord heterotopia has been frequently described. Van Gieson 1 has shown, how- 

 ever, that in a large proportion of cases the so-called heterotopia is an artefact (Fig. 

 515) and has been caused by bruises or careless handling of the cord during its removal 

 from the body or in the process of examination or hardening. 



SPINA BIFIDA. In the majority of cases hydrorrhachis is accompanied by a more or 

 less complete lack of closure of the spinal canal posteriorly, so that the collections of 

 fluid within may pouch outward through the 

 opening in the form of a sac. The sac may 

 be covered by skin, or this may be absent, 

 either from the beginning or as a result of 

 thinning and rupture. The walls of the sac 

 may consist of the dura mater and the pia 

 mater, or, in cases of hydrorrhachis externa, 

 of the dura mater alone; when both are pres- 

 ent they are usually more or less fused to- 

 gether. Inside of the membranes of the sac 

 there may be a shell of distended nerve tis- 

 sue of the cord ; or the spinal cord may be 

 split posteriorly and the sides crowded side- 

 ways; or there may be a rudimentary frag- 

 ment of the cord suspended in the sac or at- 

 tached to the walls ; or the cord may be but 

 little changed and remain inside the spinal 

 canal. The openings in the spinal canal may 

 be due to the complete or partial absence of 

 the vertebral arches, or more rarely the sac 

 may protrude through openings between the completely formed arches. Spina bifida 

 most frequently occurs in the lumbar and sacral regions, but it may occur in the dor- 

 sal or cervical regions, or the canal may be open over its entire length. Very rarely 

 it is open on the anterior surface. The protruding sac may be very small or as large 

 as a child's head. The fluid in the sac is usually clear, but may be turbid from flocculi 

 of degenerated nerve tissue. 



FIG. 515. FALSE HKTEROTOPIA. 

 FROM CERVICAL REGION OF SPIXAI 



SECTION 

 CORD. 



Showing artificial displacement of the struc- 

 tures by an experimental bruise ("false hetero- 

 topia ") after the removal of the cord from the 

 body. (Van Gieson.) 



INJURIES OF THE BRAIN. 



The brain may be directly wounded by a foreign body, or indirectly 

 by fragments of bone driven into it, or it may be lacerated by severe 

 contusion without fracture or solution of continuity of the skull. It 

 is very difficult to estimate the degree of injury which must cause 

 death, since some persons die from slight, and others recover from very 

 severe, wounds of the brain. In incised wounds of the brain more or 

 less haemorrhage occurs at the seat of lesion, and the brain tissue in the 

 vicinity soon undergoes degenerative changes. These may be compara- 

 tively slight or extensive. Inflammatory reaction may occur in the vi- 

 cinity, and the adjacent brain tissue, as well as the hsemorrhagic and de- 

 generated area, may become infiltrated with pus cells. After a time the 

 injured and degenerated area may become surrounded by new-formed 

 connective tissue, and the decomposed extravasated blood and detritus 

 1 Van Gieson, New York Medical Journal, vol. Ivi., pp. 337, 365, 421, 1892. 



