41 



PLATE XXI. 



THE FROG" continued. 



NERVOUS SYSTEM 



FIGS. I, 2. THE BRAIN or ENCEPH'ALON (Gr. en, in ; kephaJf, the head) 



rOlfactory lobes or Rhinenceph'alon (Gr. rhis, rhinos, the nose) giving off 

 I olfactory nerves. 



J Cerebral hemispheres or Prosenceph'alon ((Jr. pros, before) conii>letcly 

 1 separated by the great fissure (fig. 3). 



j Optic thalanii (Gr. thalamos, a bed), one on eacli side bounding the third 

 L ventricle with pineal gland on roof.=Thalainenceph'alon. 



MID-BRAIN ( Optic lobes above and crura cerebri (L. legs of the cerebrum) below. = 

 (Yellow) ( Mesenceph'alon (Gr. meson, middle). 



f Cerebellum (L. the little brain), very suialL=Metenceph'alon ((Jr. nitta, 

 \ behind). 



I Medulla oblongata (L. elongated marrow) with the fourth ventricle. = 

 V Myelonceph'alon (Gr. muelos, marrow). 



Lamina terminally (L. terminal plate), the anterior wall of the thalamencephalon ter- 

 minating the axial portion of the brain, the hemispheres being lateral expansions. 

 FIG. 3. THE CAVITIES OF THE DRAIN, so-called Ventricles 



1. Olfactory. 



2. Lateral . ) 



3 Tl ' -d t -1 f Aperture * communication, foramen of Munro. 



Iter a tertio ad quartum veiitriuuluui (L. passage from, third to fourth ventricle), with 



ventricles of optic lobes entering it. 



4. Fourth ventricle, continuous with central canal of spinal cord. 

 Fio. 4. GENERAL VIEW OF THE BKAIN AND SPINAL CORD, cerebro-spinal axis- 

 Brain showing chiasma (Gr. a crossing) of the optic nerves, and optic tracts leading from optic 



lobes. 



Spinal cord or myelon, tapering away to the filum terminale (L. terminal thread). 

 DIAG. 1. Ten pair of CRANIAL NERVES, ten pair of SPINAL NERVES, and ten pair of SYMPATHETIC 



GANGLIA 

 CRANIAL NERVES, 1 to 10 (yellow). 



Spinal 1, hypoglossal (Gr. kupo, under ; ylossa, a tongue), distributed to 



tongue. 



2 and 3, forming a brachial plexus (L. bmchium, an arm ; plexus, 

 a junction), and distributed to fore-limbs. 



SPINAL NERVES 

 (Blue) 



/ 4, 5, and C, distributed to the body-walls. 



7, 8, and 9, forming a lumbo-sacral plexus (L. lumlxts, the loin), 



and distributed to posterior portion of body and hind-limbs ; 

 crural to front of limb and sciatic (contraction for ischiatic) 

 to back of it. 



10, distributed to parts about coccyx. 

 SYMPATHETIC GANGLIA (S. 1 to S. 10), with connecting commissures (red). 

 DIAG. 2. CONTENTS OP NEURAL CANAL, as seen in a transverse section 



fGrey matter, a central square with its four corners passing into the 



posterior (dorsal) and anterior (ventral) roots of the nerve-trunk. 

 SPINAL CORD { Central canal lined with epithelium. 



... f Posterior fissure (dorsal). 



vV lute matter outside grey matter -; 

 l^ ( Anterior fissure (ventral). 



