10 The Structure of the Spinal Cord of the Ostrich 



masses of grey substance whose outline can be seen on the ventral surface 

 of the cord as rounded elevations, eminentiae ventrales, which bulge for- 

 ward through the ligamentous framework. There is thus formed a series 

 of hill-like prominences separated by intersegmental grooves, sulci 

 iransversi. In the grooves lie the lateral prongs of the ligamentum 

 long, ventr. From the lateral border of the segmental elevations arise 

 the motor nerve roots as a row of fine rootlets which pass through the 

 web part of the pial sheath just ventral to the ligamenta long. lat. 



On examining the lateral surface of the cord in the region from the 

 81st to 36th segment, one sees, just dorsal to the ligamenta long, lat., at 

 the level of each sulcus transversus, a small oval greyish projection meas- 

 uring 1.4 mm. long and 0.4 mm. wide. These projections are the 

 nuclei marginales majores, or the Large Hofmann Nuclei. They are 

 easily seen with the naked eye, but better with a lens and under water. 

 A description of them will be included under the heading Nerve-Cell 

 Groups. 



Caudal to the lumbo-sacral enlargement the cord decreases abruptly in 

 size and extends, gradually tapering, to the end of the spinal canal. 

 There is no cauda equina. A section of the most caudal pieces of our 

 specimen shows a central canal and a similar general arrangement of grey 

 and white matter as present in other parts of the cord. 



From Gadow's^" work we can localize the peripheral parts that are 

 controlled by this region of the cord. Gadow describes the sacral plexus 

 as consisting of three individual groups: plexus cruralis; plexus ischi- 

 adicus; plexus pudendus. The nervus sacralis, which, by means of its 

 bifurcated root, joins the latter two plexuses, he locates in the ostrich at 

 the 37th segment. The nervus furcalis, which separates the plexus 

 iscliiadicus from the plexus cruralis, he places at the 31st segment. 

 Thus the plexus cruralis is attached to the cord from the 27th to the 31st 

 segment, or the cephalic half of the enlargement. We may, therefore, 

 locate here the nerve-cell groups belonging to the trochanter muscles and 

 the muscles situated on the medial and anterior side of the femur, to 

 which area the plexus cruralis is distributed. The plexus ischiadicus 

 arises by 7 roots from the caudal half of the enlargement, the 31st to 

 37th segment. The roots of this plexus unite to form nervus ischia- 

 dicus which supplies the massive group of muscles on the lateral and 

 posterior sides of the femur and the muscles of the lower leg. Caudal to 

 the 37th segment is situated the pudendal plexus which innervates the 

 anal and genital musculature. Beyond the 43rd segment arise the deli- 

 cate caudal nerves which supply the coccygeal muscles. 



'" L. c, p. 406 



