mi: i:\< ////. i /.o.v. 



(573 



the tentorium of tlio cercbelltim pas.- B. I-,,hited from one another on 

 the middle lino by a shallower fissure, th< -e two lobes constitute the bruin, 

 iincl are usually named the cerebral hemispheres. 



In turning over the encephalon 

 mini; its inferior face, wo see 

 that the posterior peduncle of the 

 organ a continuation of the spinal 

 is prolonged beneath the ce- 

 rebellum, which is joined to the 

 lateral parts of its superior face ; 

 this portion then enters the cere- 

 bral hemispheres by their inferior 

 face, behind two thick white cords 

 the optic nerves, which mark the 

 anterior limit of this prolongation 

 ('Fig. 322). This is the igfJimu* of 

 the encenikaloH : a name given to it 

 beeaiise it actually forms an inter- 

 mediate bond between the three 

 enlargements which form the prin- 

 cipal mass of the encephalon. 



The cranial portion of the cen- 



tral nervous mass is, then, com- 



i of three apparatus: the 



i*tltiniit< of tin' encephalon, a pro- 



longation of the spinal cord; and 



,< I" Ihtiii and cerebrum, bulbous 



grafted on the superior face 



and anterior extremity of this pe- 



duncle. These three divisions are 



very well seen in their entirety 



and reciprocal relations in Figure 



\Y> will study them sepa- 



rately and in succession. 



I "I ume of the encephalon. Con- 







'.I.M.Il.U. VII.W OK 1H1. I l:\IN: I'lT: 



1. Mnlullu ol.lon^.it.i ; _', Middle \n\te of the 



.. 



< 'orol.nil hi'inisjilifi-i'-i 

 :. ''.. Kthmnidiil I. . I. nl 



lulii-s nf ditti>; 4. 4, 

 ."'. IntcrlnlaiJar t 



to what is found in the spinal 

 cord, the dimensions of the en- 

 cephalon closely represent those 

 of the cavity containing them: the 

 visceral layer of the arachnoid lying everywhere imm< diately on the proper 

 lope of the nervous mass, the, pin mater, except at the subarachnoid 

 es ; and, on the other hand, the arachnoid cavity can scarcely be said 

 to exist while the dura mater is. as it were, glued to the cranial walls, and 



titutes their internal periosteum. 



'I'll-- i ii'-ephalon has, therefore, no room to move in it- n ei pt iele, but is 

 maintained in it in an alm-st absolutely immovable condition, \\hich 



ly with that of the sutures or cranial articulations. 



WeiyliL- The total weight of the encephalon, in averau" -.-i/.< d animals, 

 may be inferred from the following figures : 1 l->rse. ~2'2 /. 1 .", diam 

 ox. 11 drams; Ox. H'> ox. 1T drams; Sheep and (mat. 1 oy. '..', drnus; Pig. 

 r, </. Id drams. J)i-g. i'i /.. .")', drams; Cat. 1 /. 1 dra!". 



In comparing ^ith those of the spinal cord, it will 1)68060 



that the relative \\eight of the medullary axis to that of tin encephalic mass 



2 \ 



