124 MAMMALIA. 



transverse fibres, forming the trapezoid body, is stretched across the upper part of the 

 oblong medulla, just below the annular tubercle ; but it is much less distinct in simise 

 than in the horse, sheep, dog, and others ; in all of them it seems to correspond with a 

 few of the transverse fibres of the annular tubercle in man, as the sixth and the hard 

 portion of the seventh in some measure originate from it. In the porpoise the 

 trapezoid body has not the same distinctness, but there is in its place a larger pro- 

 minence at the upper part of the anterior pyramidal body. 



The oblong medulla compared with the brain is generally of large size ; most of 

 its constituent parts in situation resemble the same in man, but may be larger, either 

 on account of the pedicles of the cerebellum or the more copious origin of the nerves. 

 In its general form it may be broader and thinner or thicker and more rounded. It 

 appears broader and flatter in the horse than in the ox, also in the dog and fox than in 

 the sheep and goat. Anteriorly it has in its centre the pyramidal bodies, then some 

 marks of part of the origin of the larger portion of the fifth nerve, then the restiform 

 bodies. On the posterior surface the posterior pyramidal bodies and the calamus 

 scriptorius are seen, and on each side the continuations of the restiform bodies. 



The anterior pyramidal bodies at their upper part are connected with the trapezoid 

 bodies ; the more external fibres appear to be continued down on the surface towards 

 the spinal cord, and the more inner fibres to decussate or cross each other. On 

 removing the subjacent structures the decussating inner fibres may be seen passing 

 horizontally backwards ; near the median line they are coarser, but become finer as 

 they tend to the lateral part of the oblong medulla, where they meet similar ones 

 proceeding from the inner or thicker portion of the restiform body. Superiorly the 

 fibres communicate further with the transverse ones of the annular tubercle derived 

 from the inferior pedicles of the cerebellum. 



The olivary bodies do not frequently appear distinct in shape, as in man ; they 

 are present in simise, but not so prominent. 



The posterior pyramidal bodies are nearly the same as in man : superiorly the 

 rounded ends vary in different animals ; in some, as the horse, they hardly present any 

 prominence, whilst they are very distinct in the fox. The fourth ventricle and the 



