160 CLINICAL APPLIED ANATOMY. 



When the spinal theca is invaded, symptoms due to spinal 

 nerve irritation may be met with. One such symptom is an 

 increased irritability of the hamstring muscles, and is the basis 

 of Kernig's sign. Even under normal conditions the length 

 of the hamstrings is insufficient to allow the knee to be fully 

 extended when the thigh is flexed on the abdomen, but in spinal 

 meningitis and some other conditions the range of extension is 

 still further limited. Care must be taken, when eliciting the 

 sign, that the other thigh is kept in contact with the bed, lest 

 flexion of the pelvis on the spine conceal an imperfect flexion of 

 the thigh on the abdomen and so allow fuller extension of the 

 knee. If the greatest possible angle made by the back of the leg 

 with the back of the fully flexed thigh be less than a right angle 

 and a half, Kernig's sign may be considered to be present. 



Hydrocephalus is usually secondary to posterior basic inflam- 

 mation. Sometimes it can be definitely attributed to obstruction 

 of the channels of communication between different parts of the 

 ventricular system. Such obstruction has been found at the 

 foramina of Monro causing distension of one or both lateral 

 ventricles ; in the iter, when the third ventricle is also distended ; 

 completely closing in the fourth ventricle, when the foramina of 

 communication between the ventricles and the subarachnoid 

 space are of necessity blocked ; or in the cervical region, just 

 below the foramen magnum, completely cutting off the spinal 

 from the cerebral subarachnoid space. The velum interpositum 

 may be matted to the edges of the transverse fissure, but the 

 veins of Galen are rarely occluded, so their influence in causing 

 hydrocephalus is problematical. 



Hydrocephalus often exists without any obstructions such as 

 have been mentioned. It is then due to inflammations of the 

 ventricular cavities and can be drained by lumbar puncture, 

 the fluid passing from the fourth ventricle into the space between 

 the arachnoid and pia of the cord. The spinal cord terminates 

 in the adult at the lower border of the first lumbar vertebra, but 

 in the child extends to the third. The subarachnoid and sub- 

 dural spaces reach to a point opposite the middle of the second 



