PRINCIPAL REGIONS OF SPINAL CORD 83 



Schmidt ('08) states that the Dipus (laculus), a kangaroo- 

 hke rodent, has, notwithstanding its relatively small anterior 

 extremities, a cervical enlargement which exceeds the lumbar. 

 He suggests that the size of the cervical enlargement may be 

 due to the relatively more active anterior extremity. 



A very striking illustration of the significance of the enlarge- 

 ments is given by Streeter ('03) in a description of the ostrich 

 cord. The ostrich, according to Streeter, has an insignificant 

 cervical enlargement to correspond with the almost functionless 

 wings. The 'lumbar brain,' on the other hand, extends through 

 eleven segments and its transverse section has an average area 

 of 38.5 sq. mm., which is 20.3 sq. mm. greater than the largest 

 area from the cervical enlargement. Hardesty ('05) finds a 

 similar condition in the cord of the emu, a bird closely allied to 

 the ostrich. The ostrich and emu may be taken as example« 

 in the bird family, of a condition present in the kangaroo among 

 mammalia. 



Spitzka ('86) states that the bat has an insignificant lumbar 

 enlargement to correspond with the diminutive posterior extrem- 

 ities. The specimen of bat here used (Nyctinomus brasiliehsis 

 nasutus) has a well marked enlargement in the lumbar region 

 as well as a large cervical enlargement which furnishes inner- 

 vation for its powerful wings (figs 24, C and L). Likewise, it 

 is interesting to note, as stated by Cunningham ('09), that in 

 the cetacea, although there are no visible hind limbs there is a 

 well marked lumbar enlargement. In these animals, this enlarge- 

 ment is no doubt required by the large and powerful tail. 



The grey substance 



The H shape of the grey figure, described as characteristic 

 of the human cord, holds, as is well known, for the great major- 

 ity of mammals. In the thoracic region of the bear, rhesus 

 monkey, cat, dog, lynx, and spider monkey the H is highly modi- 

 fied (Th in figs. 4, 10, 12, 14, 16, 17). In the first five animals 

 the peculiar shape consists in a shortening or flattening of the 

 dorsal horns and a relatively very wide grey commissure. The 

 almost complete absence of the dorsal horns in these animals 



