XIII 



PTTYLTM CHORDATA 



;',2'.t 



thickened mass of iieivc-inattci 

 and between them 

 passes a transverse 

 band of nerve-fibres, 

 the anterior commis- 

 sure (a.c). The dien- 

 cepliahn is a small 

 rounded lobe between 

 the paraco'los and the 

 mid-brain, and con- 

 taining a laterally 

 compressed cavity, the 

 diaccele (v.S). Its roof 

 is extremely thin. Its 

 lateral walls are 

 formed of two thicken- 

 ings, the opfie tlialami, 

 behind which passes 

 a transverse baud, the 

 jjosterior com missu) -e 

 (p c), Behind aud 

 below the thalami 

 are the optic tracts 

 (o. t.) continued into 

 the optic nerves. Be- 

 hind the optic tracts 

 the floor is produced 

 downwards into a 

 tubular process, the 

 infundihulum {inf-), 

 ending below in a 

 rounded body, the 

 pituitary hody or hypo- 

 physis {p)ty.). The roof 

 is produced into a 

 median process, the 

 epiphysis (Fig. 070, D, 

 pn; Fig.07l,ir), which 

 is divided into two 

 parts, one of which 

 has connected with its 

 distal extremity an 

 e3''e-like structure, the 

 parietal organ or 

 pineal eye (Fig. 971, 

 ixi), lying in the parietal 

 in the velum transversum 



m.o 



Firi. !iVO.— Brain <■£ Z<acerta viridis. A, fiorn above, with 

 the left pareiiceplialoti (f. h.) and uptic lobe (o. /.) opened. 

 B, frcjm beneath. C, from the leftside. D, in longitudinal 

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

 duct of Sylvius ; cb. ccreljellum ; <: c. ci'ura cerebri ; c. Ii. 

 cerebral hemispheres; ch.p. choi-oid plexus; c.s. corpus 

 striatum ; f. ni. foramen of Mom-o ; inf. ii.fundibuluni ; 

 ill. 0. medulla oblongata ; o. c. optic chiasma ; o. !. optic 

 lobes ; olf. olfactory bulbs with their peduncles or tracts ; 

 o. t. optic tracts; o. v. apeiture between aqueduct of 

 Sylvius and optic ventricle ; p. c. posterior commissure ; 

 pn. pineal body ; /ifi'. pituitary body ; v3, diaccele ; r4, 

 metacce ie ; I— XII, cranial nerves. (From Parker's 

 Zootoni}/.) 



foramen. In front 

 (v. t.), a transverse 



of the epiphysis, 

 fold of the thin 



