ANATOMY IN A NUTSHELL. 335 



and fibers which carry impulses for inhibition of reflex action. The vasomotor 

 and inhibitory fibers pass to the motor cells of the anterior horn. When the 

 crossed pyramidal tract degenerates these inhibitory and vasomotor fibers are 

 included, and dilatation of the blood vessels and increased reflexes result. 



In spina bifida there is an overbundance of cerebro-spinal fluid with faulty 

 development of the posterior walls of the lumbar portion of the spinal canal. 

 In this condition the membranes are pushed through the opening in the spinal 

 canal by the weight of the cerebro-spinal fluid. 



The subarachnoid spaces of the cord and brain are continuous and connected 



PLATE CLY. 



3. PLEXIUS OF CAPILLARY BLOOD-VESSELS WITHIN THE LOBULE. 



1. INTERLOBULAR VEINS . « R 1 V. 2. INTRALOBULAR VEIN. 



4. TWIGS OF INTERLOBULAR VEIN, PASSING TO THE ADJACENT LOBULES. 



The Vessels of a Lobule of the Liver. 



with the fourth ventricle by the foramina of Magendie, Key, and Retzius. 

 The opening of a spina bifida may drain the cerebro-spinal fluid from the brain 

 and result in fatal convulsions. 



The fissures of the cord are antero-median. postero-median, two antero- 

 lateral, two postero-lateral. and two dorso-intermediate fissures. These fissures 

 divide the cord into eight columns, viz.. ventral, lateral, "Goll, ami Burdack 

 (posterior.)" These are on each side. 



The ascending and descending fibers of the white matter of the cord 

 arranged in tracts, but these tract- are not recognizable in the adult cord, but 

 only during development or when affected with disease or degeneration. The 

 facts concerning the tracts have been ascertained by embryologies! and path- 

 ological research. This division of fissures is somewhat arbitrary, a- the place 

 where the anterior nerve roots leave the cord i> not always called a fissure, and 

 the dorso-intermediate one is only in the cervical region. If we lake this di- 

 vision there are only eight fissures and eighl columns in the spinal cord. The 

 antero-median fissure extends about one-third the diameter of the cord, toward 



