PHYSIOLOGY : PRACTICUM VIII : PLATE XXI. 



LFFT SIDE OF THE SHEEP'S BRAIN AFTER -THE REMOVAL OF MOST OF 

 THE CEREBRUM AND CEREBELLUM ; X i. 



myel 



po'ns postoblongata 



oV 



The CEREBELLUM is left of its natural height, but the cephalic and caudal convexi- 

 ties are sliced away so as to expose the parts which are overhung by them. In a compan- 

 ion preparation the dorsal portion of the cerebellum has also been removed, with the 

 cephalic and caudal convexities, but the lateral "overhangs" are retained. 



The CEREBRUM has been cut down to the level of the THALAMI ; the caudal por- 

 tion cut away along the oblique line of its projection over the part marked 5 ; the lateral 

 portion so as to expose the part marked 3 ; also the cephalic projection which, as seen in 

 Plates XIX and XXV, overhangs the OLFACTORY BULBS. 



The short lines on the surface of the olfactory bulb represent the OLFACTORY 

 NERVES. The cut end of the left OPTIC NERVE is dotted to indicate its fibrous structure. 



i, OLFACTORY CRUS ; compare with PI. XX. 2, a part of the PALLIUM which has 

 not been cut. 3, OLFACTORY TRACT. 4, (indistinct), CHIASMA. 5, PREGENICU- 

 LUM (external or anterior geniculate body), distinct in man but here little more than a 

 lateral portion of the thalamus. 6, TUBER (cinereum), the slight convexity to which 

 the HYPOPHYSIS is attached ; in PI. XX it is the area just caudad of the chiasma. 7, 

 the MEDIPEDUNCLE, continuing the PONS to the lateral mass of the cerebellum. 6, 

 the TRAPEZIUM ; compare with PI. XX. 



Excepting the unshaded areas, representing cut surfaces, all the parts seen in this fig- 

 ure were covered by PIA. 



At the dorsal end of the cerebellum are seen a few FOLIA, its leaflet-like divisions ; 

 these are not shown in any other plate. 



Besides facilitating the recognition of certain important parts this figure well illus- 

 trates the segmental constitution of the brain, which is obscured in the entire organ by the 

 preponderance of the cerebrum and cerejaellum. There is a series of more or less distinct 

 masses demarcated by constrictions of greater or less depth. Admitting that there is still 

 some doubt as to number and limits of the segments the following assignments may be ac- 

 cepted provisionally : 



Olfactory bulbs and crura, \ RHINENCEPHAL. 

 Cerebrum }- PROSENCEPHAL (fore brain). 



Thalami, conarium, hypophysis, j DIENCEPH AL (inter-brain), 

 chiasma, and geniculums, ( 



Geminums and crura \ MESENCEPHAL (mid-brain). 



Cerebellum, pons and preoblongata, \ EPENCEPHAL (hind-brain). 



Postoblongata | METENCEPHAL (after-brain). 



