CHAP. X 



BRAIN 



159 



Clf.v 



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

 nerves. (A C, after Gaupp ; D, from Wiedersheim's Comp. Anatomy, 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 Her, ihe third ventricle 

 (v 3 ), the sides of which are 

 formed by thickenings of 

 nervous matteV, the optic 

 thalami (Di), connected by 

 transverse bands of nerve- 

 fibres (D, com). On the 

 ventral surface the dien- 

 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 body 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. 



\-Sp.cd 



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 ; 

 Lat. v. lateral ventricle ; Med. 

 obi. medulla oblongata; Nv. i, 

 olfactory nerve ; Olf. L. olfactory 

 lobe ; Olf. v. olfactory ventricle ; 

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

 ventricle ; Sp. cd. spinal cord ; 

 v. 3, third ventricle ; v. 4, fourth 

 ventricle. (After Ecker & Wie- 

 dersheim.) 



