OF THE EUMINANTIA. 



57 



opposite side. The same bundle ia twice in the external, but 

 only once in the internal layer ; hence it is that the outer layer 

 contains twice as many fibres as the inner layer ; it is not, how- 

 ever, twice as thick, because it contains much less cellular tissue 

 than the inner layer, and is, in consequence, more compact than 

 that layer. 



The fact which must more especially be borne in mind is, that 

 the bundles of the inner layer, when traced either upwards or 

 downwards, always decussate at the nearest decussation ; and 

 when traced onwards in the outer layers they form the non- 

 decussating bundles at the next decussation. If this fact be for 

 a moment thought over, it will be seen how impossible it is to 

 draw from it any but the above conclusion as to structure, viz. 

 that the bundles form perfect looj)s, crossing the gullet three 

 times (Fig. 6). The manner in which the loops are linked 



Fig. 6. 



Drawing from a model made*with an india-rubber band upon a cylinder of 

 wood. It shows the essential element in the structure, viz. a continuous ban d 

 of fibres crossing the oesophagus three times ; it begins at a (which is a line of 

 decussation) on one side, and ends at b (the other line of decussation) as a 

 '«o?i-decussating bundle on the other side. At A, b, and e', e, it is in the outer 

 layer ; it decussates at c and d, between wliich, f, f, it is in the inner layer ; so 

 that it is twice in the external, but only once in the internal layer : it decus- 

 sates at both decussations c and d, and also forms non-decussating bundles at 

 both A and b. 



together, so as to form a continuous tube, is extremely ingenious. 

 A diagram will, however, explain the arrangement better than 

 any description (Fig. 7). 



Fig. 7. 



Drawing from a model made with three india-rubber bands instead of one, to 

 show how the bands are connected one to another. 



M^hen the band 1 is decussating for the second time at a', the band 2 begins 

 as the non-decussating bundle, which, it will be observed, is external to the 

 decussating bundles ; as the second band runs round to the opposite decussation, 

 b', it gets in below the first band, which ends at b' (external to the second bundle) 

 as the «on-decussating bundle. In the drawing, the first band has been folded 

 round the second band between a' and b'. The same arrangement as that 

 described occurs when a third band is added (between a" and b '), and so on. 



The fii'st tm-n of the first band (a) and the last turn of the thii-d band (b'") 

 are necessarily incomplete, owing to the want of other bands. Between a and 



