XIII 



PHYLUM CHORDATA 



405 



developed olf:ictoiyori;-an : <iii tlic otlicr liaml, ilic optir nerves and 

 tracts are of unusual si/,(\ 



The spinal cord (Fig. 1040, .s/\ (v/.) presents large brachial and 

 lumbar enlargements from which the nerves of the fore- and 

 hmd-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 simis 



o.c 



■>.c- 



l.t, / 



o-rlv. v^ ijif O.C. m.o. 



Fif!. 1041".. — Cclumba livia. The brain. A, with the cavities opened from above ; B, in 

 sagittal seution. u.<\ anterior commissure; ch. cerebclUim ; c.h. cerebral hemispheres; 

 c.s. corpus striatum ;/. m. foramen of Monro; tn/ infundibuhun ; m.o. medulla oblongata; 

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

 o. V. optoc(cle ; p peduncles of cerebellum ; p. c. posterior commissuie ; pn. jiineal body ; 

 tlic. diencephalon ; v. ii, diaoele; v. A, metaccele. (From Parker's Zootomi/.) 



rJwinhoidalis (s. rhh.), 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 turhincds, 

 which greatly increase the surface of mucous membrane. The 

 anterior portion of the cavity, including the anterior turbinal, 

 is coverecl by laminated epithelium and serves as a vestibule ; 



VOL. II C C 



