REPORT ON THE SEALS. Ill 



both of the tentorium and cerebral hemispheres upon an elongated structure, like the 

 pineal stalk, would occasion atrophy both of the stalk and of the pineal eye, and a con- 

 secpient disappearance of the mesial parietal foramen in the mammalian skull. It is 

 conceivable, however, that the atrophy might begin distally by bone formation closing up 

 the parietal foramen, as a result of which both eye and stalk would disappear. But what- 

 ever cause has been in operation to lead to the disappearance of both pineal eye and stalk, 

 only the proximal end of the pineal organ, where it arises from the thalamencephalon, is 

 left in the Mammalia. It is, however, of interest to note that in at least one Mammal, 

 viz., the Walrus, this proximal part may retain such magnitude as to be visible between 

 the hinder ends of the cerebral hemispheres, so that it does not present so aborted or 

 residual a character as in other Mammals. But the special function, if any, which may 

 be discharged by the pineal body in this animal will be difficult to ascertain. 



The Cerebellum was a massive organ and consisted of a middle lobe and of two 

 lateral lobes or hemispheres. The middle lobe on the tentorial surface was separated by 

 a furrow on each side from the corresponding lateral lobe, and the distance from this 

 furrow to the extreme lateral border of the hemisphere was 54 mm. At the superior 

 margin of the cerebellum the middle lobe was concealed in a cleft which separated the 

 two hemispheres from each other. Inferiorly where the middle lobe formed the roof of 

 the 4th ventricle it was depressed between the two lateral lobes of the cerebellum. Each 

 hemisphere was divided into a tentorial and an occipital part by a vertical transverse 

 fissure, and the surface of the tentorial aspect was split up into numerous broad plate- 

 like folia by intermediate fissures. The occipital aspect was similarly subdivided, but 

 there was also evidence of a division of this aspect into lobelets by broader fissures. 

 Thus about opposite the middle of the side of the medulla oblongata a broad and deep 

 fissure curved outwards and forwards, so as to divide this aspect of the cerebellum into 

 an anterior and a posterior lobelet. The folia which bounded the fissure dipped into it in 

 a whorl-like manner, so that the fissure may be distinguished as the vorticose fissure (v). 

 On raising the anterior lobelet the superficial transverse fibres of the pons could be traced 

 without any difficulty into the white core of the hemisphere. 



The Pons Varolii was broader in the middle than either in front or behind. It had 

 the usual mesial groove for the basilar artery, and the superficial transverse fibres were 

 very distinct, and could readily be traced outwards into the hemispheres of the 

 cerebellum. The 5th nerve arose from the side of the pons by a large sensory and a 

 small motor root. The motor root was at first on the inner side of the sensory, and then 

 passed outwards in contact with its ventral surface to join the inferior maxillary division 

 of the ganglion. The sensory root was 1 3 mm. in its transverse diameter, and expanded 

 anteriorly into a flattened Gasserian ganglion which gave off the three divisions of the 

 nerve ; some fibres of this root entered the substance of the pons, but others passed 

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



