CHAP. X 



BRAIX 



159 



cerebri ; Di. diencephalon ; for. M. foramen of Monro ; i. iter, or aqueduct of 

 Sylvius ; inf. infundibulum ; Med. obi. medulla oblongata ; Olf. L. olfactory 

 lobe ; opt. cA.opticchiasma ; Opt. 1. optic lobe ; opt. v. optic ventricle ; pin. stalk 

 of pineal body ; pit. pituitary body ; Sp. cd. spinal cord ; v 3 . third ventricle ;. 

 ir. fourth ventricle ; I X, cerebral nerves ; / Sp. 2 Sp. first and second spinal 

 nerves. (A C, after Gaupp ; D, from Wiedersheim's Comp. A natomy, after 

 Osborn.) 



like the posterior choroid plexus, of a thickening of 

 pia mater, containing numerous blood-vessels. It helps 

 to roof over a narrow slit- 

 like cavity communicating 

 with the iter, the thirdventride 

 (t t3 ), the sides of which are 

 formed by thickenings of 

 nervous matter, the optic 

 thalami (Di), connected by 

 transverse bands of nerve- 

 fibres (D, com). On the 

 ventral surface the dien- 



Clf.v 



crff 



Cfltt 



Mid obi 



c.C 



[-Sjh.ee/ 



cephalon is continued into a 

 funnel-like extension, the 

 infundibulum (Fig. 49, inf), 

 to which is attached a 

 rounded structure, the 

 pituitary body (pit). On the 

 dorsal surface, just behind 

 the choroid plexus, is . the 

 delicate stalk (pin) of the 

 pineal bodv the vestige of a 

 sensory apparatus between 

 the skull and the skin, which 

 in some lizards, for example, 

 has the structure of a small 

 eye situated on the top of the 



head, and which was probably functional in the an- 

 cestors of the frog. We shall meet with other examples 

 of such vestigial organs in the course of our studies. 



FIG. 50. Diagrammatic horizontal 



section of Frog's brain. 

 c. c. central canal ; Cer. H. cerebral 

 hemisphere ; Di. diencephalon ; 

 for. M. foramen of Monro ; i. iter ; 

 Lot. v. lateral ventricle ; Med. 

 obi. medulla oblongata : .V;-. /, 

 olfactory nerve ; Olf. L. olfactory 

 lobe ; Olf. v. olfactory ventricle ; 

 Opt. I. optic lobe ; Opt. v. optic 

 ventricle ; Sp. cd. spinal cord ; 

 i . j. third ventricle ; v. 4, fourth 

 ventricle. (After Ecker & Wie- 

 dersheim.) 



