130 PROFESSOR DAVID HEPBURN ON 



higher levels presented the ridges and depressions which are the characteristic of the 

 claustrum, and it was only after the sections had passed below the level of the general 

 mass of the lenticular nucleus that the claustrum was seen as a separate structure, with 

 a definite external capsule between it and the more deeply placed grey mass. Indeed, 

 the appearance of striation, which was directed forwards and outwards, was more 

 definite below the level at which the lenticular nucleus still retained its biconvex 

 outline and while the striated substance intervened between the claustrum and the 

 head of the caudate nucleus. The effect of this disposition of the grey and white 

 masses of the corpus striatum was to suggest that the differentiation of the external 

 capsule was incomplete and had not advanced to the stage of separating the claustrum 

 from the lenticular nucleus. 



A band of white substance intervened between the cortical grey matter and wavy 

 margin of the claustrum, and, since the claustrum is usually regarded as a detached and 

 submerged portion of the grey cortex of the insula, it would appear the white fibres 

 which separate the grey cortex from the claustrum are developed earlier than those 

 which, in the higher brains, separate the claustrum from the caudate nucleus and are 

 known as the external capsule. In TURNER'S account of the elephant seal, it does not 

 appear that he submitted his specimen to this dissection. The grey nature of the tail 

 of the caudate nucleus was always distinct, and an extension of the sections through the 

 optic thalamus revealed quite plainly its grey substance, bounded laterally by the 

 posterior limb of the internal capsule. The grey matter, however, did not resolve itself 

 into the subordinate nuclei (anterior, mesial, and lateral) which characterises the 

 human brain. 



Tlie Pineal Body. I was able to examine three specimens of this interesting object, 

 and in each case it presented widely different characters. Indeed, the differences were 

 so pronounced that they were not easy to reconcile and certainly not easy to explain. 



In the brain which I removed from the skull of the seal which was two days old 

 at the time of its death, the pineal body was a large prismatic object resting upon the 

 vermis of the cerebellum and wedged into the interval between the occipital ends of 

 the cerebral hemispheres. It projected about 27 mm. behind the splenium of the 

 corpus callosum. The peduncle broke in the process of removal, but it was very short 

 and apparently just sufficiently long to permit the expanded part to clear the splenium. 

 The dimensions of the expanded, prismatic part were as follows : greatest length, 

 27 mm. ; width, 18 mm. ; vertical depth, 12 mm. 



In a second specimen, belonging to one of the adult brains, the peduncle was again 

 broken, but the expanded part still occupied its natural position. In this case the 

 peduncle was cylindrical and the expanded end was pyriform in shape, its measurements 

 being : length, 20 mm. ; width, 15 mm. ; vertical depth, 9 mm. It showed no signs of 

 faceting by pressure from surrounding structures, as might have been expected, 

 supposing the reduction in its size as compared with the young specimen to have 

 resulted from the effects of preservative solutions. In the third specimen, also that 



(ROY. SOC. EDIN. TRANS., VOL. XLV1II., 842.) 



