112 THE VOYAGE OF H.M.S. CHALLENGER. 



medulla oblongata. The 6th nerve had been torn away in a and c, but in b was 

 situated in the groove between the pons and anterior pyramid. The 7th or facial nerve 

 arose from between the pons and medulla external to the anterior pyramid. The 8th 

 or auditory nerve arose from the lateral aspect of the medulla immediately behind the 

 pons. 



The Medulla Oblongata or Bulb was much injured in specimen a, but in good order in 

 the two others. It possessed on each side of the mesial fissure a distinct anterior pyramid 

 which passed above into the substance of the pons. Immediately external to this pyramid 

 but not reaching the pons was an elongated oval swelling 14 mm. long and 4 mm. in 

 greatest transverse diameter; this swelling was bounded both on its inner and outer borders 

 by a shallow groove. The roots of a nerve, which were unfortunately torn across in c 

 close to the medulla, emerged from the groove at the inner border ; in b they were entire 

 and were the roots of the hypoglossal or 12th cranial. The swelling is to be regarded 

 as like the olive in the human medulla, where the hypoglossal nerve arises from the 

 groove on its inner side between it and the anterior pyramid. In Phoca vitulina a 

 swelling was also seen in the same region but not separated by a groove from the anterior 

 pyramid so that it is a part of that structure. External to the upper end of the anterior 

 pyramid was a body which apparently represented the trapezium, though it was not 

 marked with transversely arranged bundles of nerve fibres. Below this body the side 

 of the medulla swelled out into a restiform body, the surface of which was marked by 

 arciform fibres running from before backwards around the side of the medulla. Springing 

 out of the restiform body were some nerve roots, which in c were torn across close to the 

 medulla, but were entire in b, and were the origins of the 9th, 10th, and 11th cranial 

 nerves. Of these nerves the 11th or spinal accessory was large, and its spinal roots were 

 traced for a short distance along the side of the cord. The dorsal surface of the medulla 

 was hollowed out into the 4th ventricle, which was prolonged forwards on to the corre- 

 sponding surface of the pons. 



Nothing is known of the development of the convolutions and fissures in the 

 cerebrum of the Walrus, and I have not met with any description of the order in which 

 the convolutions and fissures appear in the hemispheres of the Seals. Some years ago I 

 was presented by one of my pupils, Mr. T. G. Ker, with twin foetuses of Phoca grcen- 

 landica which he had extracted from the uterus of the mother, when acting as surgeon 

 on a ship engaged in the Seal fishing. The foetuses were preserved in rum, and after 

 they came into my possession I removed the brains. The length of the foetus from the 

 snout to the tip of the pes was 222 mm. The cerebrum was 20 mm. long and 22 mm. 

 wide. The cranial surface of each hemisphere was quite smooth, except that about the 

 junction of the anterior and middle thirds a very shallow furrow passed from the mesial 

 longitudinal fissure transversely outwards for 8 mm.; it seemed to be a slight tear on 

 the surface (PI. VIII. fig. 4). Low down on the outer side of the hemisphere a shallow 



