EXPLANATION OF TBE PLATES. 463 



PLATE II. 



§ 1161. Fig. 3. — The basis encephali, or ventral aspect of the brain ; x 2. 

 Compare with Fig. 116. 



The proportions and general features are from the brain of an adult 5 , Maltese and 

 white. Prep's 288, 289. Some details of the Area praechiasmatica (the region cephalad 

 of the chiasma) are from 461 and 527 ; of the Ar. postpontilis (the region caudad of the 

 pons) from 358, 454 and 491 ; and of the intermediate Ar. cruralis from 432, 506 and 527. 



Most of the nerves and cerebral fissures are lettered on the right side, and most of the 

 other parts on the left. Some of the left nerves are cut short, and the left N. trochlearis 

 is not shown at all. 



The Lobi olfactorii {LI. ol.) are made too long, and the hypophysis {hph) is too short. 



Attention is called to the following points, chiefly in comparison with the human 

 brain : — 



The absence of a distinct Radix intermedia [Rx. in.) of the Crus olfactorium, corre- 

 sponding with the so called " middle root of the olfactory nerve " in man. The part so 

 designated upon the plate is apparently only an area, comparatively undifEerentiated, 

 between the more or less fibrous tracts forming the Radix mesalis and Rx. lateralis. 



The turning of the Bx. mesalis {Rx. ms.), (" internal root "), over the margin of the 

 brain so as to appear upon the meson. 



The distinction of the Rx. lateralis {Rx. I.), {" external root "), into a lateral gray and a 

 mesal white tract, the Limes cinerea {Lm. cin.) and the Lm. alba. 



The great extent of the (Locus) praeperforatus {prpf.), and its division into a cephalic 

 more prominent portion {Pt. p.) and a caudal depressed portion {Pt. d.). Both portions 

 are " perforated," but the degree of furrowing of the Pt. 2irominens varies considerably. 

 These furrows exist in some other Carnivora. 



The width of the hypophysis (hph.) and the crenation of its caudal border, indicating 

 the existence of an ental subspherical mass, which is covered by an ectal layer, the thin- 

 ness of which, in the caudal region, permits the contour of the former to be seen. 



The slight degree of separation of the albicantia [abn.), which are here nearly con- 

 cealed by the hypophysis, but more fully shown in Fig. 12. 



The distinctness of the cimbia (cmb.), which is better seen in Fig. 11. 



The slight extent of the true postperforatus (ppf.) ; the only part which is really 

 " perforated " is a small area just caudad of the albicantia, and partly hidden by them. 



The less caudo-cephalic extension of the pons (pn.) ; this exposes more of the Area 

 intercruralis (Ar. ic.) than in man, and uncovers the trapezium {tz.), which, in man, is 

 wholly concealed. Connected also with this feature of the pons is the fact that the N. 

 abducens {N. abd.) passes directly cephalad from its origin a little caudad of the pons, 

 whereas in man it is forced to curve aroand the caudal border. Finally, the N. trigemi- 

 nus (If. trg.), instead of emerging through the pons near the cephalic border as in man, 

 emerges close to its caudal border or clears it completely ; see Chap. XI. 



The greater extent of the Ar. cruralis, which may be ascribed both to the less extent 

 of the pons and the less degree of flexure of the whole brain at the mesencephalic region. 



The greater width of the Tractus postrhinalis (JV. prh.), which includes the surface 

 of the Lobulus hypocampae (LI hmp.). In man, indeed, this part is hardly visible on 

 account of the prominence of the convolutions laterad of the F. postrhinalis. 



The apparent origin of the iV. oculomotorius (N. oem.) laterad of the meson and just 

 caudad of the cimbia (cmb.). 



