;///: f/:.\ y/M/. .t.\/> <>r mi: .\i:i;v<>t s >>->'/'/ .ir 



<jl<ui(lit: small appended lobes pL eel one on the superior, the other on tho 

 inferior face of the isthmus. 1 



Fig. ;;J-'. Medulla Oblongata. (Figs. 323, 



324, 329.) 



The mcdiiHit nliloityttta constitutes 

 tho posterior portion of the encephalic 

 isthmus; it succeeds tho spinal cord, 

 and extends forward as far as the pons 

 Varolii. It is a thick peduncle of a 

 white colour, wider before than behind, 

 flattened above and below, and having 

 four faces an inferior, superior, and 

 two lateral. 



Inferior face (Fig. .322). This 

 face rests in the channel of the basilar 

 process. Convex from side to side, 

 and limited anteriorly by a transv 

 fissure which separates it from the 

 pons Varolii, posteriorly it does not 

 offer anything to distinguish it from 

 the medullary axis. 



On the middle line there is a well- 

 marked fissure, a continuation of the 

 inferior fissure of the cord, which lies 

 between two very elongated promi- 

 nences that are sometimes but little 

 apparent, and from their form are 

 named the pyramids of the bulb (corpora 

 pyramidalia) (Figs. 322, 19 ; 338, 6). 

 The base of these pyramids touches 



1. Olfactory lobe ; ti, Cavity of the olfactory tlle P ons Varolii, and their apex is 



lobe ; 3, External root of olfactory lobe ; insensibly lost, posteriorly, on roach- 



4, 5, Cerebral hemispheres; 6, Cerebellum ; ing the spinal cord. 

 7, Optic chiasma, or commissure ; 8, Pitui- Outwardly is an almost plane sur- 



t.-u-y gland; 9, Optic nerves; 10, Tuber , i )or( i or(J( l im fori ( ,rlv bv -i ti-ins 



cinereum; 11, Crus cerebri; 12, Third l CC ' U 



cranial nerve ; 13, Fourth nerve ; 14, Pons verse band which lies immediately 



Varolii; 15, Fifth nerve; 16, Sixth nerve; behind the pons Varolii; sometimes 



17, Seventh and eighth nerves; 18, Me- Jt { s covered for the greater part of its 



dulla oblongata the number being placed extent b ft thiu cxpans i on (lf 



on the olivary body ; 19, Anterior pyramid ; . '.,, 



20, Roots of ninth, tenth, and eleventh arciform fibres, between the anterior 

 nerves; 21, Twelfth nerve. border of which and the transverse 



1 There is far from being any agreement as to the numlM-r of purls which oujrht to 

 compose the encephalic isthmus, some authorities making more, some less. The limits 

 of this small apparatus will, nevertheless, be found perfectly circumscribed if it be ex- 

 amined in the lower animals, nnd particularly in the Horse. An antem-posterior section 

 of the encephalon made to one side of the median piano np|>ears to ns all that is needed 

 t ' definitely settle the point. This section, seen in figure li'jy. shows in the plainest 

 manner that the encephalic prolongation of the spinal axis extends to the corpora 

 -trial. i. and that it comprises the medulla oblongatu. IMHIS Varolii, cerebral and ccrebi-Mar 

 peduncles (or crunv), the corpora quadrigemina. and the thalami optici. All these, then, 

 belong to one and the same system -the medullary peduncle, which serves as a bond 

 of union between the three principal n,a>-os of the encephalon, and which we hav 

 designated the ixlhmus. It may ! adih d that this manner of considering the enivplud 

 isthmus perfectly agrees with the teachings of physiology. 



<;I;NI:I:AI. VIKW ov Tin; I;I:AIN; IXDWKR 



SL-UKACK. 



