8 . The Structure of the Spinal Cord of the Ostrich 



dural sheath, leave the spinal canal, and form the spinal nerves, as is 

 described under the heading Meninges. Owing to the fact that the roots 

 have a short intravertebral course, leaving the canal directly, a bundle 

 of them forming a cauda equina is not here present, and the nerves thus 

 correspond in position to the segments of the cord and to the vertebrae. 

 There are in our specimens 51 pairs of nerves. We may classify the 

 nerves and segments after the morphology of the vertebrae as follows : 



The topography of the cord is represented in Fig. 3. It will be 

 observed that corresponding to the wings and legs the cord is in two 

 places increased in size, the brachial and Iwtibo-sacral enlargements. 

 The former is so barely visible that one notices at first only the enor- 

 mously developed lumbo-sacral enlargement. A more careful observa- 

 tion however discloses a slight increase in size in the region lying be- 

 tAveen the 16th and 19th pairs of nerves. The difference in size is much 

 more apparent in cross-sections. 



Fiirbringer * describes the plexus brachialis of the ostrich as made up 

 of the spinal nerves arising from the 17th to 21st segments, and this cor- 

 responds to our cervical enlargement. It is this region, therefore, that 

 we must think of as the sensory and motor center for the wing muscula- 

 ture. 



The remainder of the cervical and thoracic portion of the cord is 

 nearly uniform in size, and on section shows a rounded circumference. 

 A fissura ventralis longitudinalis is to be seen, but dorsally in this region 

 no fissure is present. The segments in a way are marked off at the 

 attachment of the spinal nerves by a slight dorso-ventral compression and 

 a corresponding increase in size laterally. 



In the lumbo-sacral region an entirely different appearance is pre- 

 sented. It is in this region of the cord that the crural and sacral plex- 

 uses are attached which supply nerve-fibres to the leg. The system of 

 reflexes which is necessary for the control of the massive musculature of 

 this member demands a large accumulation of nerve-cells and comiecting 

 nerve-fibres, and this accumulation forms the lumbo-sacral enlargement, 

 the so-called " Lumbar Brain." As is stated above, the lumbo-sacral 



" Ftirbringer, Untersuchungen zur Morphologie und Systematik der Vogel. 

 Theil I., Amsterdam, 1888. 



