XIII 



PHYLUM CHORDATA 



307 



olf 



-c.h 



m.o 



(Fig. 915, c. h.) are oval bodies, somewhat narrower in front than 

 behind, closely applied 

 together. Each is pro- 

 longed anteriorly into 

 the corresponding ol- 

 f ad or ij lobe (olf. /.), a 

 club-shaped process 

 from which the olfac- 

 tory nerve arises. In 

 the interior of each is 

 a cavity, the lateral 

 c< utricle or paraccele, 

 sending a prolonga- 

 tion forwards into the 

 olfactory lobe, and 

 communicating be- 

 hind by a small aper- 

 ture, the foramen of 

 Monro (D,/. m.), with 

 the diaccele (v.3). 

 Through the foramen 

 of Monro there passes 

 into each paraccele a 

 vascular process of pia 

 mater, the choroid 

 plexus (cli. p^). On the 

 floor of each paraccele 

 is a thickened mass 

 of nerve-matter, the 

 corpus striatum (c.s.), 

 in front of which 

 passes a transverse 

 band of nerve fibres, 

 the anterior commis- 

 sure (a. c.). The dien- 

 ceplialon is a small 

 rounded lobe between 

 the paracceles and the 

 mid-brain, and con- 

 taining a laterally 

 compressed cavity, the 

 diaccele (v. 3). Its roof 

 is extremely thin. 

 Its lateral w^alls are 

 formed of two thick- 

 enings, the optic thalami, between which passes across a transverse 

 .band, the posterior commissure, (p. c.). Behind the thalami are the 



x 2 



v4 



m.o 



FIG 915. Brain of Lacerta viridis. A, from above, with 

 the left parencephalon (c. It.) and optic lobe(o. I.) opened. 

 B, from beneath. C, from the left side. D, in longitudinal 

 vertical section, a. c. anterior commissure ; aq. s. aque- 

 duct of Sylvius; cb. cerebellum; c. c. crura cerebri ; c.h. 

 cerebral hemispheres; ch. p. choroid plexus; c. s. corpus 

 striatum ; /. in. foramen of Monro ; inf. infundibulum ; 

 m. o. medulla oblougata ; o. c. optic chiasma ; o. I. optic 

 lobes ; olf. olf actory lobes ; o. t. optic tracts ; o. v. aperture 

 between aqueduct of Sylvius and optic ventricle ; p. c. 

 posterior commissure ; pn. pineal body ; pty. pituitary 

 body ; r3, diaccele ; v4, metacoele ; I XII, cranial nerves. 

 (From Parker's Zootomy.) 



