George L. Streeter 11 



Arrangement of White and Grey Substance. 



A cross-section of the cord shows, in a general way, a central four- 

 horned area of grey matter surrounded by a much larger area of white 

 matter. The two dorsal horns of grey matter separate off a portion of 

 the latter forming the dorsal funiculi, so called in distinction to the re- 

 mainder of the white matter, or ventro-lateral funiculi. The entline 

 and relative size of these individual areas in different levels of the cord 

 are shown in Fig. 3. 



A great variation exists in the size of the dorsal and ventral horns, 

 as well as the anterior commissure. These structures are apparently 

 closely interrelated, as they undergo the size-variation in unison. All of 

 them reach their greatest development in the lumbo-sacral enlargement. 

 Of the ventral and dorsal horns, the latter show less increase in size in 

 the two enlargements. In the cervical region the dorsal horns are re- 

 duced to a narrow strand of grey matter and fail to reach the border of 

 the cord. The white commissure, commissura ventralis, connecting the 

 two halves of the cord is present at all levels, and will be described more 

 in detail in connection with the fibre tracts. The grey commissure from 

 the 31st to the 36th segments entirely fails. Its place is filled by the tis- 

 sue of the sinus rhomboideus. 



A more exact knowledge of the total area of transverse sections made 

 at different levels, and the relative area of the antero-lateral funiculi, the 

 dorsal funiculi, and the grey substance was obtained by a method which 

 allows the calculation of the areas in square mms. 



In this method one makes a series of outline drawings (in our case the 

 Edinger drawing apparatus was used) of the various segments on a sheet of 

 evenly-rolled lead or tin foil. Thick cardboard can also be used when the 

 drawings are large. The drawings of the individual segments thus out- 

 lined on the sheet of lead are all magnified on the same scale. A drawing 

 is also made in a similar way and with the same enlargement of a square 

 cm. which has been outlined in ink on a glass slide. The drawings of 

 the different segments and of the square cm. are then cut out from the lead 

 sheet, and the segments further cut apart into the different areas. These 

 pieces are all separately weighed. The ratio then, between the weight of each 

 individual part and the weight of the piece representing the square cm., is 

 equivalent to the area of this part. 



Sections were taken from each segment of the ostrich cord, and the area of 

 the various fields was thus calculated. The sections were taken uniformly 

 near the departure of the nerve to avoid the discrepancy that might occur 

 from differences in the same segment. This variation in the upper part of 

 the cord is hardly appreciable. In the lumbo-sacral enlargement, however, 

 it is more marked, and we have a distinct segmental character given to the 

 cord by the increase in the size of the ventral horns, which occurs in the 

 middle of the segment. Taking the sections at the level of the roots has the 



