NERVOUS SYSTEM. VKRTEBRATA. 495 



D. 768. The sacral and caudal parts of the spinal cord of an 

 Ostrich, showing the enlargement which takes place at the 

 point of origin of the nerves for the hind limbs, and tho 

 lateral separation of the posterior columns of the cord at 

 this part, leaving an interspace the "sinus rhomboidalk" 

 The cavity of this space in Birds is filled by a cellular ma-. 

 derived apparently from the ependyma of the central canal. 

 The following is the original description of this prepa- 

 ration : " The part of the medulla which lies in the loins 

 and tail of an Ostrich. That part which lies in the loins 

 is considerably larger than those which belonged to tin- 

 neck and back ; and then it becomes pretty fast smaller to 

 the tail. This swelling in the loins is owing, perhaps, to 

 this bird having such large thighs and legs ; and when we 

 consider that this bird, having such small wings, must have 

 the whole progressive motion performed by the legs, and 

 the legs are therefore longer in proportion to the size of tin- 

 bird than in birds in common, we must see why the medulla 

 ought to be large at this part in this bird." 0. C. 1." 



Hunierian. 



D. 769. The hinder part of the crural swelling and the caudal 

 part of the spinal cord of an Ostrich, with the membranes 

 partially reflected showing, upon the ventral surface, the 

 origins of some of the motor roots of the nerves to the 

 legs. The dorsal longitudinal fissure is shown in the cauda 1 

 part. There is never in Birds a cauda equina due to the 

 shortening of the spinal cord in relation to the vertebral 

 column. 0. C. 1356. Hunierian. 



D. 770. The attenuated caudal prolongation of the spinal cord 

 of an Ostrich. 0.0. 1357. Hunterian. 



D. 771. The brain and spinal cord of a Partridge (Perdix ru/a) 

 exposed in situ from above. This specimen shows clearly 

 the relative proportions of the different regions of the cord : 

 the long cylindrical cervical segment ; the fusiform swelling 

 at the origin of the brachial plexus ; the relatively short 

 thoracic portion; the crural swelling, with its open rhomboid 

 fossa ; and the rapid diminution of the cord behind the 

 sacrum The cord almost completely fills the cavity of the 

 neural canal. 0. C. 1358. Hunterian. 



