Ingbert, Ventral Roots of Spinal Nerues. 233 



(c) Relation of the Area of the Cross-sections of Four Roots in 

 the Brachial and in the Lumlio-sacral Plexuses. 



Brachial (C. V— VIII) Lumbo-sacral (L. IV, V & SI, II) 



2 males 56.42 mm.^ 45.40 mni.^ 



2 females 47.32 mm.- 50.70 mm.^ 



Hence we can conclude in that in the two males the area 

 of the cross-sections of these four roots of the branchial plexus 

 is better developed than that of the four roots of the lumbo- 

 sacral plexus, while in the two females the reverse relation holds 

 true. Although these results are based on too small a number 

 of cases to establish fully a relation of such importance, they 

 are very suggestive, and may serve as a basis for further investi- 

 gation. 



Summary. 



(\) AREAS OF ROOTS. 



1. The total area of the cross-sections of the ventral roots 

 of the left spinal nerves of a large man was found to be 

 26.50 mm.- (Table I). 



2. Since the total area of the cross-section of the ventral 

 roots of the left s'pinal nerves is 26.50 mm.-, and that 

 of the dorsal roots 54.93 mm.-, the ratio of their areas 

 is 1:2.07 (Table V, p. 212). 



3. In the cervical region, the third ventral root and the 

 fourth dor.sal are interesting because of the diminution 

 in their areas, as well as in the number and diameter of 

 their fibers (Page 225). 



4. In the dorsal roots the area of the cross-sections is pre- 

 dominantly a function of the number of fibers, while in 

 the ventral roots the area of the cross-section of the 

 roots is chiefly a function of the size of the fibers 

 (page 225 ). 



5. The largest ventral roots arise one to two segments 

 cephalad to the largest dorsal roots, and the ventral 

 cervical depression (C. Ill) is one segment cephalad to 

 the dorsal cervical depression (C. IV) (page 224). 



6. In two male cords the sum of the areas of the four 



