THE ANATOMY OF THE WEDDELL SEAL. 133 



expansion backwards as well as laterally, and a reduction in the size of the flocculus, 

 biventral lobe, and the tonsil, would be capable of producing a cerebellum with practically 

 the same superficial characters as that of man. 



The pons Varolii was well developed, and measured 25 mm. from its anterior to its 

 posterior border in the line of its very definite basilar groove. The anterior and 

 posterior borders converged upon each other so rapidly, as they travelled outwards to 

 form the middle cerebellar peduncles, that the outline of the posterior border was 

 interrupted by the emergence of the large root of the 5th cranial nerve. As a result 

 of this arrangement, the greater part of this nerve-root made its appearance from the 

 side of the medulla oblongata between the olivary eminence and the pons, but of course 

 close up to the latter. In the elephant seal TURNER notes that the 5th cranial nerve 

 arose from the pons Varolii and not from the bulb, whereas, in describing the same nerve 

 in the walrus, he remarks that some fibres of the sensory root " passed backwards 

 between the facial and auditory nerves to the anterior and outer part of the medulla 

 oblongata." 



The medulla oblongata was wide at its upper end, where it measured 40 mm. ; but 

 it narrowed rapidly towards the lower end, and instead of being conical it was markedly 

 flattened in the dorso-ventral direction. Its upper or " open " part was associated with 

 the 4th ventricle, while the "closed" or lower part contained the central canal in its 

 unexpanded condition. Its bilateral character was indicated by the anterior and 

 posterior medium fissures, the former shallow and terminating in relation to the 

 posterior border of the pons Varolii at the foramen of Vicq d'Azyr. On each side of 

 the anterior median fissure or groove the pyramid formed quite a distinct tract. The 

 point of emergence of the 6th cranial nerve was not between the pyramid and the 

 pons as in man, but from a flattened area situated external to the pyramid, so that the 

 nerve-stem made its appearance close to the mesial side of the large medullary root of 

 the 5th nerve and without any fibres of the pons intervening between them. The 7th 

 and 8th cranial nerves emerged from the side of the medulla oblongata close behind 

 the 5th and 6th nerves, but slightly nearer the dorsal or ventricular aspect of the bulb. 



The olivary eminence was small and not so prominent as in man, but it distinctly 

 separated the 9th and 10th cranial nerves from the 1 2th or hypoglossal nerve. 



The closed part of the medulla oblongata presented the general appearances and 

 proportions of the adjacent part of the spinal cord as regards its fissures and main 

 columns. Posteriorly, the funiculus gracilis with the clava at its upper end, the 

 funiculus cuneatus with its upper expansion, the cuneate tubercle, and also the tubercle 

 of Rolando were all definitely recognisable. They turned outwards in a common bundle 

 from a point immediately below the obex, and skirting the infero- lateral margin of the 

 4th ventricle they entered the cerebellum as the restiform body or inferior cerebellar 

 peduncle. The visible decussation of the pyramids began at a point 32 mm. from the 

 hinder margin of the pons Varolii, so that we may consider the total length of the bulb 

 to be distinctly less than its width at its upper end. 



(ROT. soc. EDIN. TRANS., VOL. XLvin., 845.) 



