206 DISSECTION OP THE DOG 



In the cervical region the dorsal funiculus is divided into a fasciculus 

 gracilis [Golli^ and a, fasciculus cuneatus [Burdachi]. 



Encephalon. — It is best to begin the examination of the brain by a 

 general inspection of its external conformation. The brain in its entirety has 

 an ovoid shape, the broader, caudal end being formed mainly by the medulla 

 oblongata and the cerebellum, but partly also by the cerebral hemispheres. 

 The compressed oral extremities of the cerebral hemispheres, capped by 

 the olfactory bulbs, constitute the narrow end of the ovoid. Of all the com- 

 ponent parts of the organ, the cerebral hemispheres are far and away the 

 most bulky, and it is these which contribute the greatest transverse diameter. 

 When the brain is viewed from the dorsal aspect little more than the hemi- 

 spheres is visible, though a part of the cerebellum may be seen as well as a 

 small section of the medulla oblongata. A longitudinal fissure (fissura longi- 

 tudinalis cerebri) separates the two hemispheres, while a transverse fissure 

 divides the hemispheres and the cerebellum from each other. 



On looking at the brain from the ventral aspect a considerable number 

 of structures are distinguishable. Of these, the most important only need 

 be mentioned here. The rest will be exammed in the proper place. Con- 

 tinuing the spinal cord at the aboral end of the brain is the medulla oblongata, 

 a dorso-ventrally flattened column somewhat similar to the spinal cord in 

 external appearance. Immediately in front of the medulla there is a broad, 

 transverse band, the pons, which can be readily followed laterally into the 

 cerebellum. Appearing at the oral border of the pons are two thick, rounded 

 cords, the cerebral 'peduncles, which, after a diverging course, disappear into the 

 cerebral hemispheres. Between the two peduncles is a depression, the inter- 

 peduncular fossa (fossa interpeduncularis [Tarini]), containing a white eminence, 

 the mammillary body, and a grey promiaenee, the tuber cinereum. With the 

 latter, the hypophysis is connected by the hollow stalk-like infundibulum. 

 The optic tracts approach each other and finally blend at the optic chiasma, 

 which lies immediately in front of the tuber cinereum. The rest of the ventral 

 view is occupied by parts of the cerebral hemispheres. 



A lateral examination of the brain reveals little more than the hemispheres 

 of the cerebrum, with partial views of the cerebellum, pons, and medulla 

 oblongata. 



Meninges. — Of the three membranous coverings of the brain, the dura 

 mater has already been examined. 



Aeachnoidea encephali. — Continuous with, and structurally similar to 

 the corresponding membrane of the spuial cord, the arachnoid of the brain 

 is, for the most part, closely related to the pia mater. It does not, however, 

 follow the pia into the fissures of the cerebrum, and at the base of the brain 

 the relation of the two membranes is much less intimate than elsewhere. 



