AN ANOMALY IN THE INTERNAL COURSE OF 

 THE TROCHLEAR NERVE. 



By Richard Weil. 



With Plate HI. 



Although variations in the course and distribution of the ex- 

 ternal portion of the Trochlear nerve are by no means unknown 

 the present case represents, as far as the writer has been able 

 to discover, the only recorded instance of an internal anomaly. 

 This is probably to be attributed to the relative infrequency 

 with which histological examinations of the internal structure 

 of the midbrain are made. It is certainly true that the mor- 

 phological peculiarities of this nerve — embracing the character 

 of its cells of origin, of its decussation, of its exit, and also of 

 its development — mark it as the most aberrant of the cranial 

 nerves, and might lead a priori to an expectation of considerable 

 variability. 



The material' was a human foetus, of the eighth to the 

 ninth month, of which one-half the brain above the medulla 

 was preserved in bichromate, and stained according to the Wei- 

 gert procedure. The bundles which took the stain in the mid- 

 brain were the nerves : oculomotor, trochlear, and trigeminus ; 

 the long sensouy tracts : superior and inferior fillets, and the 

 posterior longitudinal bundle, and some of the intracerebral 

 commisural tracts, such as the brachium conjunctivum. The 

 origin of the trochlear nerve is, as normally, in the floor of the 

 Sylvian aqueduct, dorsal to the posterior longitudinal bundle. 

 All the fibers are given off in one or two bundles, and run 

 obliquely dorsally and backwards to the decussation. The re- 

 lations of the nerve in this part of its course, both to the mes- 

 encephalic root of the fifth nerve and to the superior brachium 



ipor this I am indebted to the Pathological Laboratory of the New York 

 State Hospitals. 



