16 The Structure of the Spinal Cord of the Ostrich 



fashion. In the 30th segment the sulcus extends the entire distance to 

 tlie grey commissure completely separating the dorsal funiculi and form- 

 ing the cephalic end of the sinus rhomboideus. At this level a change 

 in the character of the glia^hows itself in that part of the peripheral 

 sheath between the ventral and dorsal nerve roots, as well as in the 

 grey commissure and the adjoining divided septum dorsale. In these 

 places instead of a compact mass of fibres the glia shows a looser and 

 more sponge-like appearance. In the succeeding sections this glial modi- 

 fication rapidly increases in extent, coincident with the increase in the 

 size of the sinus, and reaches its maximal development between the 30th 

 and 36th segments. A drawing from this region is reproduced in Fig. 5, 

 and a portion of the glial web is shown under higher magnification. It 

 is thus seen that the peripheral glia sheath throughout the circumfer- 

 ence of the cord, except at the attachment of the ligamenta denticulata, 

 is changed into, or replaced by, a tissue consisting of enormous cells 

 (.003 to .004 mm. in diameter), the body of each of which is filled with 

 a transparent fluid of undetermined nature which crowds the small 

 nucleus to one side, or the nucleus is suspended in the fluid supported by 

 a slender stalk of cell tissue. It resembles fat tissue to some extent. 

 It however fails in frozen section to stain with Herxheimer's solution 

 of Fettponceau. In iron-hgematoxylin picro-fuchsin preparations there 

 is no trace seen of connective tissue fibres. The cells remained unstained 

 like the neuroglia cells of other parts of the section. By exclusion, then, 

 we are led to consider them as modified neuroglia cells, though we un- 

 fortunately lack the definite evidence of a selective stain. 



The sinus rhomboideus of birds has always been an object of interest 

 to investigators, especially as to the character and significance of the 

 gelatinous material with which it is filled. Of the earlier writers the 

 work of Duval " may be referred to, the results of which were more or 

 less confirmed recently by Kolliher.^' Both of these authors from em- 

 bryological evidence agree as to the glial nature of the tissue filling the 

 sinus. They, however, do not make mention of the presence of this web- 

 like material around almost the entire circumference of the cord. 



The grey commissure and the septum dorsale are entirely changed 

 into this tissue, which thus fills the sinus as a broad network separating 

 the blunt ends of grey substance and the dorsal funiculi and extending 

 ventralward to the commissura ventralis. In the ventral part lies the 



" Duval, L. c. 



^-Kolliker, Ueber die oberflachlicheu Nervenkerne im Marke der Vogel und 

 Reptilien. Zeitschrift f. wiss. Zool., LXXII, 1. 



