347 



by the addition of vesicular substance. Anteriorly the cords are 

 separate and continuous with the pharyngeal crura of their respective 

 sides ; but through the rest of their course they lie in close contact 

 along the middle line. The ganglionic enlargements vary somewhat 

 in size, shape, and approximation at different parts. The vesicular 

 substance is on their under surface, and consists of about two strata 

 of cells continuous in a lamina across both cords. Along their 

 borders, however, the cells form a thicker layer or column, which 

 extends for some distance along the intervening cords. In form and 

 general appearance the cells are similar to those of the pharyngeal 

 chain, but many of them are larger. Those of the first ganglion extend 

 into the lower parts of the crura, and are continuous behind with the 

 lamina of the second. Each ganglion gives off from its sides two 

 pairs of nerves, which, after sending some filaments to the septa and 

 muscular bands, supply the longitudinal, oblique and circular muscles 

 of the rings. Midway between the ganglia, the intervening cords 

 give off a single pair, which are distributed to the deep muscles on 

 each side. Within the ganglia the roots diverge in three different 

 ways : 1, longitudinally ; 2, transversely ; and 3, to the grey or 

 vesicular substance. The first or longitudinal form a large portion of 

 the nerves, and run in equal numbers in both directions backwards 

 and forwards, along the whole breadth of the corresponding cord. 

 In their course, some of them, near the border, separate in succession 

 from the rest and enter the lateral columns of cells ; others proceed 

 as far as the next nerve, with the roots of which they form loops, 

 and pass out, while the rest continue onwards and, perhaps, in suc- 

 cession form similar loops with distant nerves. In former communi- 

 cations to the Royal Society, the author has shown that the same 

 kind of arrangement exists in the spinal cord of Man and Mam- 

 malia. 



The second or transverse order of fibres are less numerous, and in 

 general less distinct than the last. They proceed from the middle 

 of each opposite root, and cross the cords directly ; but some of 

 them, on reaching the opposite cord, turn round in both directions, 

 and run with its longitudinal fibres. In front of the first ganglion, 

 in which they are unusually distinct, a separate band unites the roots 

 which descend from the branches arising from the opposite crura of 

 the pharyngeal collar. 



