REPORT ON THE SEALS. 101 



more compactly enclosed in a common envelope of connective tissue. The Gth nerve, 

 about equal in size to the same nerve in man, arose from the posterior border of the pons 

 in the groove between it and the anterior pyramid. 



Medulla oblongata or Bulb. — The Bulb was sharply differentiated above by the groove 

 between it and the pons, but the demarcation between it and the spinal cord below was 

 not so clear, for the decussation of the pyramids was not very distinct in the ventral 

 longitudinal fissure. On each side of this fissure a definite anterior pyramid was seen, 

 much more distinct where it entered the pons than near the spinal cord. On each side of 

 this pyramid was a slight ovoid elevation which was continuous with the anterior pyramid 

 on its inner side, but was more clearly defined on its outer border by a shallow fissure. 

 Outside this elevation and in the interval between it and the pons the trapezium was 

 very distinct. The restiform body formed a definite elevation on the side of the medulla. 

 The dorsal surface was hollowed in the usual way into the 4th ventricle, which was 

 prolonged forwards to the dorsal surface of the pons. The 7th or facial nerve arose 

 immediately behind the sensory root of the 5th from the groove between the pons Varolii 

 and the trapezium. The 8th or auditory nerve arose immediately behind but lateral to 

 the 7th, from the outer part of the trapezium in close relation to the cerebellum ; as it 

 passed outwards it grooved the ventral surface of the hemisphere of the cerebellum. The 

 9 th or glossopharyngeal nerve arose immediately behind the auditory from the outer part 

 of the trapezium. The 10th or pneumogastric nerve arose by a number of distinct fasciculi, 

 some of which were situated mesial to the others ; they were placed behind the glosso- 

 pharyngeal and passed outwards in relation to the ventral surface of the hemisphere of 

 the cerebellum. The 11th or spinal accessory nerve was a cord of considerable magnitude; 

 its roots arose from the side of the medulla behind the pneumogastric and also from the 

 side of the cervical cord between the anterior and posterior nerve roots. The roots of the 

 12th or hypoglossal nerve came out of the medulla at the fissure which marked the outer 

 border of the ovoid elevation above referred to, so that this " elevation " can scarcely be 

 regarded as the homoloorie of the " olive " which in the human medulla lies to the outer 

 side of the roots of the hypoglossal nerve. 



Arteries of the Brain. — Two vertebral arteries converged and joined on the ventral 

 surface of the medulla oblongata to form the basilar. From each vertebral two small 

 spinal arteries passed backwards in relation to the ventral surface of the spinal cord, and 

 a much larger branch, a postero-inferior cerebellar, was distributed to the posterior part 

 of the occipital surface of the cerebellum. The basilar artery ran forwards mesially, at 

 first in relation to the ventral surface of the medulla oblongata, and then to the corre- 

 sponding surface of the pons as far as its anterior border. When in line wdth the posterior 

 border of the pons the basilar gave off a pair of large branches, antero-inferior cerebellar, 

 which passed outwards to supply the more anterior part of the occipital surface of the 

 cerebellum. As it lay in the groove in the pons several small transverse branches arose 



