24 The Structure of the Spinal Cord of the Ostrich 



tralis we may state the fact that a longitudinal ventro-dorsal section 

 cut through the commissura ventralis, from the 32nd to 34th segment, 

 shows that the commissure here is practically imiform in the ventro- 

 dorsal diameter. It presents no segmental increase in size at the levels 

 of the Hofmann'sche Kerne which would be expected if the size of the 

 commissure in the lumbo-sacral enlargement were due to the presence of 

 these nuclei. 



Fibre Tracts. 



Myelinated fibres are present both in the grey and white substance 

 of the cord. In the former they are seen in the preparations in cross 

 and longitudinal section, and form a network which cannot be resolved 

 into definite fibre tracts. 



The great bulk of the spinal cord fibres make up the white matter, 

 and form a thick envelope surrounding the grey substance. This en- 

 velope may be separated into ventral, lateral and dorsal funiculi. The 

 boundary between the first two is an artificial one, produced by the 

 fibres of origin of the ventral nerve roots. At levels where those fibres 

 are few or absent there is no point of division between the two funiculi. 



The dorsal funiculi are more sharply defined. They are separated 

 from each other by the septum posterior, and separated from the lateral 

 funiculi by the dorsal horns and the glial processes which extend from 

 the tip of the horns to the peripheral sheath of the cord. 



The general variation in size and shape of the dorsal funiculi occur- 

 ring at different levels of the cord can be seen in Fig. 3. The definite 

 area is recorded by a table and by Fig. 4, in which a diagram gives the 

 area in a curve indicating square mms. Thus a further mention of the 

 shape and size of these funiculi is here not necessary. 



In their finer structure the dorsal funiculi consist of fibres of en- 

 trance and departure, and fibres having a longitudinal course. The 

 bundles of fibres entering as the dorsal nerve roots vary greatly in size, 

 as is seen macroscopically. Those in the lumbo-sacral enlargement are 

 two or three times larger than those in the cervical enlargement, and 

 about five times larger than those of the upper cervical region. These 

 fibres enter obliquely as a compact bimdle at the dorso-lateral border of 

 the funiculi. The bundle then breaks up into loose strands, disappear- 

 ing among the longitudinal fibres. No fibres could be seen to enter the 

 grey matter directly. In longitudinal sections most of the fibres could 

 be seen to bend upwards, and could be traced a short distance in the 

 longitudinal direction. A few fibres were seen which, on entering, turned 

 caudalwards. In neither Van Gieson nor Weigert prej)arations, how- 



