. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative. Fifi. 135.âTbansvekse Section through the Fobe Part of the Teleosteax Brain. fr, frontal bone, underneath which the pineal tube, Gp, is visible in transverse sec- tion, and below this the pia mater, Pm; Pa, the pallium, or roof of the sec- ondary fore-brain, formed of a simple epithelial layer ; , prosocrele ; Ep, ependyme ; T, T, olfactory tracts at the base of tlie corpora striata (). Dipnoi.âBoth as regards external and internal structure, certain points of resemblance may be seen between the brain of Dipno
. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative. Fifi. 135.âTbansvekse Section through the Fobe Part of the Teleosteax Brain. fr, frontal bone, underneath which the pineal tube, Gp, is visible in transverse sec- tion, and below this the pia mater, Pm; Pa, the pallium, or roof of the sec- ondary fore-brain, formed of a simple epithelial layer ; , prosocrele ; Ep, ependyme ; T, T, olfactory tracts at the base of tlie corpora striata (). Dipnoi.âBoth as regards external and internal structure, certain points of resemblance may be seen between the brain of Dipnoans and that of Elasmobranchs on the one hand and Amphibians on the other. This fact probably indicates that though the Elasmobranchii and Dipnoi have arisen from a common ancestral type, they have become differentiated along different lines. The prosencephalon is well de- veloped (Fig. 136): the thin pallium is mainly nervous, and is involuted along the median longitudinal line so ^â ^*gjLJfcC^''' "c*' as to completely separate the two â ^^^ 11Wi^v^'e^'^ '^ hemispheres from one another in Protopterus: in Ceratodus they are // \1I\V\ ' *^"' united together posteriorly by a narrow 7 I ij y^ol commissure. Olfactory lobes arise ' from the prosencephalon anteriorly, and contain ventricles. The thalamencephalon of Pro- topterus presents certain very charac- teristic features, especially as regards its roof The pineal body has a long stalk, and its distal vesicle perforates the cartilaginous roof of the skull: in the embryo Ceratodus it even )eaches as far as the integument. The choroid plexus gives rise to a vesicular organ, and as regards its. TTved, Fig. 136.âBrain of Ceratodus fosteri. Dorsal view. (From ParkerandHaswell's Zoology.) and, auditory nerve ; rlj/, cere- bellum ; fac, facial nerve ; rjl, glossopharyngeal; med, me- dullaoblongata;mes',mesence- phalon; oc, oculomotor nerve; opt, optic nerve ; pros, cere- bral hemispheres; rh, olfac- tory lobes ; vij, vagu
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