26 The Structure of the Spinal Cord of the Ostrich 



and descending cerehellar tracts by experimental secondary degenera- 

 tion in doves. 



The ventral funiculi have an inner zone which is a ventral extension 

 of the inner zone of the lateral fnnicnli. The outer zone, tractus cere- 

 bello-spinalis ventralis medialis of Friedlander, is somewhat larger, and 

 forms a more or less triangular field, of which the fissura ventralis forms 

 one side. The fibres of this field are all large and average 1.5 /x, many 

 of them being over 2 fi. In the Imnbo-sacral enlargement the enormous 

 increase in size of the ventral and lateral funiculi seems due to an acces- 

 sion of smaller fibres which are added to the inner zone, and this increase 

 is more marked in the ventral than in the lateral funiculus. 



A commissura alha anterior of ol)liquely crossing fibres is present at 

 all levels of the cord, connecting the two ventral funiculi. It is greatly 

 increased in size between the 28th and oGth segments. A sagittal sec- 

 tion through the commissure in this region does not show any segmental 

 grouping of these fibres. In Weigert preparations strands of fibres 

 can be traced through the commissure coming from the outer zone of 

 tlie ventral funiculus and extending to the opposite ventral horn. We 

 have here doubtless a motor tract from higher centers, the fibres of 

 which decussate before ending about the cells of origin of the motor 

 nerve roots. The large number of ventral horn-cells in the lumbo- 

 sacral enlargement woidd thus partly explain the large size of the com- 

 missure which here prevails. No trace of commissural fibres dorsal to 

 the grey commissure was found in any of our sections. A posterior 

 white commissure is apparently lacking. 



resume'. 



In looking back at the more important characteristics presented by 

 the spinal cord of the ostrich, a feature to be first referred to is that in 

 its mass the cord forms by far the largest part of the central nervous 

 system. In other words, then, we have here an animal the various 

 parts of whose body receive their principal innervation from the spinal 

 cord, and the influence of the brain on these parts is secondary and 

 remote — an animal that works chiefly with its primary apparatus. 



This suggestion as to the important part played by the primary ner- 

 vous complex is further confirmed by the fact that the grey substance 

 and associating collaterals vary in amount at different levels accordinfj 

 to the demands made by the parts supplied. Thus throughout the cer- 

 vical cord where there is a small and uniform number of neck muscles 

 to be supplied the primary apparatus presents a correspondingly small 



