22 Tlie Structure of the Spinal Cord of the Ostrich 



rudimentary, the Hofmann'sche Kleinkerne. The third or scattered group is 

 made up of cells similar to the lateral group cells of the ventral horns, and 

 occurring at irregular points on the periphery of the ventro-lateral funiculi, 

 more especially near the exit of the ventral nerve roots and near the Hof- 

 mann'sche Grosskerne. Kolliker considers these cells to he detached elements 

 from the ventral horns. 



In the ostrich the occurrence and arrangement of peripheral cells is 

 similar to that found by Kolliker and Ijachi in the dove and hen. In 

 describing them we follow Kolliker's classification, but would substitute 

 more descriptive names. 



The nuclei 'marginal es majores (Lobi accessori. — Lachi : Hofmann'sche 

 Grosskerne. — Kolliker) lie on each side of the cord Just dorsal to the 

 ligamenta longitudinalia lateralia at levels marked off by the sulci 

 transversi ventrales. Of these nuclei fi pairs could be readily seen with 

 the naked eye. They appear as elongated oval greyish semi-translucent 

 elevations measuring macroscopically 1.0 to 1.4 mm. long. The inter- 

 val between successive nuclei averages 6.0 mm. Each segment of the 

 lumbo-sacral region was cut in transverse or longitudinal series, mostly 

 the former. In studying these sections this nucleus was identified in 

 the 30th, 31st (32d injured in removing the cord), 33d, 34th, 35th, 

 and 36th segments. Thus the nucleus occurs in the region of the sinus 

 rhomboideus, extending a little cephalad as well as somewhat caudad to 

 it. Microscopically in the preparations the nucleus is seen projecting 

 from the lateral border of the cord Just dorsal to the attachment of the 

 ligamentum denticulatum, as is represented in Fig. 5. 



The size of the nuclei averages among the larger ones .10 to .18 mm. 

 antero-ventral diameter, and .08 to .13 mm. lateral diameter. In a 

 continuous series of sections 20 /x thick the nucleus is present in 62 ; 

 that is the nucleus is 1.24 mm. long. These dimensions are somewhat 

 smaller than the macroscopic, as could be expected from shrinkage 

 associated with the embedding process, and possibly partly due to greater 

 accuracy in measuring, the l^oundaries of the nuclei being more definite 

 in the prepared and stained specimen. 



The free border of the nucleus is overlapped by pia, and the inner 

 border merges gradually into the wliite substance of the cord. It con- 

 sists of a network of glia tissue, somewhat looser and more vascular than 

 the adjoining cord. In this sponge-like framework lie a number of 

 multipolar nerve-cells and myelinated axis-cylinders. The cells resem- 

 ble those forming the lateral group of the ventral horn, but are not 

 more than one-fourth to one-sixth as large. In one nucleus 10 of 

 these were seen in which the cell nucleus was cut throug-h. In the 



