106 STUDY OF A HUMAN SPINA BIFIDA MONSTER WITH 



with the angle directed posteriorly must have occurred in the midbrain region. 

 At the beginning of the spinal cord a bend in the opposite direction is present. 

 This bending of the brain stem and cord must have been in lateral outline shaped 

 like a crudely drawn letter Z, as shown in figure 24, which is a diagram of various 

 structures in the central nervous system near the midline. The surface of the 

 inverted fourth ventricle floor is shaped like an isosceles triangle with its tip, 

 which is its normal anterior end, directed backward toward the encephaloceles. 

 The median sulcus is well defined. The tissue next to the median sulcus on both 

 sides is slightly raised. The rest of the surface is flat. For estimating roughly 

 the amount of distortion this fourth ventricle floor had undergone, a comparison 

 of it with the fourth ventricle floor of three normal full-term fetuses was made. 

 Each of the three showed a similar longitudinal ridge to be the extent of their surface 

 markings. The main difference which this specimen showed seemed to be in a 

 blunting of the posterior end which forms the base of the triangle already referred to. 



From both lateral margins of the fourth ventricle floor cortical tissue resembling 

 the flocculus is drawn backward, downward, and to the right, joining the cerebellar 

 cortex contained in the right sac. It must be noted that while the flocculus is 

 directed toward the posterior end of the specimen as a whole, it is drawn toward 

 the end of the ventricle floor normally anterior. There is a much disturbed choroid 

 plexus folded in with the cerebellar tissue. A fairly large amount of cerebellar 

 tissue is present; part of this is drawn out into a sheet which is continuous with the 

 flocculus and which passes posteriorly and to the right into the right encephalocele, 

 where it lies next to a rounded mass of cerebellar cortex. Bands of tissue con- 

 necting the cerebellum and cerebrum probably represent the brachium conjunc- 

 tivum. There are smaller flat bands of tissue passing backward near the flocculus 

 to the rounded cerebellar cortex which may have been remnants of the inferior 

 cerebellar peduncles. There is no pontine enlargement. 



From the tissue superior to and continuous with the floor of the fourth ven- 

 tricle, the third and the fifth to the twelfth paired cranial nerves pass forward to 

 their normal exits from the subdural space. They are elongated to between 20 

 and 30 mm. Their origin from the brain-stem lies opposite the first thoracic verte- 

 bra. In this region the beginning of the flattened cord can be made out, which is 

 bent double upon itself. Some interest is attached to this Z bend of the brain-stem 

 and cord. It seems to have been brought about in this case through traction 

 on these parts by the major portions of the central nervous system slipping 

 through the enlarged foramen magnum. Varying degrees of such kinking have been 

 described. The condition in its milder forms has received the name of Chiari 

 deformity, from a case described by Chiari in which the medulla is bent back over 

 the cord for only a short extent. In Nageli's case of cyclopia there is a marked 

 degree of such bending associated with splitting of the cord. 



Caudal to the bend as a flat band the spinal cord extends to the level of the 

 lumbar vertebra, where it terminates in a cauda equina. From its ventral surface 

 the spinal nerves extend into the dura. At the level of the twelfth thoracic vertebra 

 the spur in the vertebral plate has left an indentation on the flat cord and on the 

 right anterior third of the inverted floor of the fourth ventricle. 



