xrn 



PHYLUM CHORDATA 



405 



developed olfactory organ : on the other hand, the optic nerves and 

 tracts are of unusual size. 



The spinal cord (Fig. 1040, sp. cd.) presents large brachial and 

 lumbar enlargements from which the nerves of the fore- and 

 hind-limbs respectively are given off. In the lumbar enlargement 

 there is a divergence of the dorsal columns of the cord converting 

 the central canal into a wide, diamond-shaped cavity, the sinus 



C.7l 



f* 



olf 



FIG. 1046. Columba livia. The brain. A, with the cavities opened from above; B, in 

 sagittal section, a. c. anterior commissure ; cb. cerebellum ; c. h. cerebral hemispheres ; 

 c. s. corpus striatum ; /. TO. foramen of Mpnro ; inf. infundibulum ; TO. o. medulla oblongata ; 

 o. c. commissure of optic lobes ; o. ch. optic chiasma ; o. 1. optic lobes ; olf. olfactory bulbs ; 

 o. v. optoccele ; p peduncles of cerebellum ; p. c. posterior commissure ; pn. pineal body ; 

 the. diencephalon ; v, 3, diacuele; v.lt, metacoele. (From Parker's Zootomy.) 



rho'inboidalis (s. rJib.\ bounded above only by the membranes 

 of the cord. 



Sensory Organs. The olfactory organs are paired chambers in 

 the base of the beak, separated from one another by the meseth- 

 moid and bounded externally by the ecto-ethmoid. The latter 

 is produced inwards into three scroll-like processes, the turbinals, 

 which greatly increase the surface of mucous membrane. The 

 anterior portion of the cavity, including the anterior turbinal, 

 is covered by laminated epithelium and serves as a vestibule; 



VOL. II C C 



