The sympathetic ganglia appear to be en tirely composed of structures siinilar to those first described, imbedded in a more or less granular transparent blastema.
In embryos of 6 to 8 inches in len,gth, the sympathetic ganglia still contain a large num of If inches in length. The sympathetic cord and branches present the same structure. In the ganglia of the cerebro-spinal nerves, the ganglionic corpuscles are larger and more dis tinctly formed than in the sympathetic ganglia. Arany of the cells have processes similar to those above described; and in several of these, at a short distance from the corpuscle, there is a small oval nucleus such as K011iker describes in the human embryo of 16 inches. The nerves belonging to the cerebro-spinal system are also much further developed than those in the sympathetic. Those in the bra chial plexus present the appearance of being composed of a slightly-granular transparent blastema, marked by longitudinal strim, and containing embedded in it oval granular nuclei. The strim are arranged parallel to one ano ther, and evidently correspond to the margins of the nerve-fibres. The nuclei are arranged at intervals, and occupy the entire breadth of the fibres. There is no trace of the %%bite substance of Schwann.
ber of corpuscles similar to those in earlier embryos. There are also present a number of bodies larger than these, and consisting of a distinct cell-wall inclosing, besides a nucleus, a finely-granular fluid. They are commonly round ; some are more or less egg-shaped. The nucleus in the latter is generally situated towards the wider extremity of the cell, while its narrow end is prolonged into a delicate, granular process about the wi,5-0-th of an inch in breadth. The nerves in the gan glia do not differ much in appearance from those in the Gasserian gan,glion of the embryo In the sympathetic ganglia of embryos measuring 18 or 19 inches in length, there are still present a considerable number of granular corpuscles measuring from the „1,--,th to the ,-,1„th of an inch in diameter, similar to those already- described. They are chiefly com posed, however, of cells resembling those in the ganglia after birth, only smaller and more delicate. The nerve-fibres in the ganglia have much the same appearance as those already described in the brachial plexus of embryos frorn 6 to 8 inches in length. In the ganglia
occurring on the posterior roots of the spinal nerves, the Gasserian ganglion, and the gan glion on the trunk of the pneumo-gastric, the ganglionic corpuscles differ from those in the perfect animal only in point of size. Most of the nerve-fibres connected with the ganglia present the same tubular character as the perfect nerve-fibre. The nerve-fibres in the roots of all the cranial nerves present the dis tinctly tubular character also ; in those of the 3rd, 4th, and 7th, the double contour is more the nuclear character, similar to those already described in connection with its ganglia, and representing an early stage of the development of the cerebro-spinal nerve-fibres. Addition of dilute solution of soda brings into view a few tubular nerve-fibres similar to those in the spinal nerves. The splanchnic nerves present the same structure as the cord of the sympathetic, containing a few tubular nerve fibres, but being chiefly composed of the other structures. In one of the nerve-filaments from the surface of the right ventricle of the heart, or less distinctly visible. The optic nerve con sists of fine tubular fibres mingled with small round or oval bodies. The nerve-fibres in the brachial plexus also present the character of perfect tubular fibres ; they are narrower than in the adult animal. So also the fibres in the trunk of the pneumogastric ; throughout the entire extent of the trunk of this nerve, in the neck and upper part of the thorax, there were embedded amongst its fibres ganglionic corpuscles similar in their character to those occurring in the ganglia of the cerebro-spinal nerves. Sometimes a single corpuscle lay imbedded in a bundle of nerve-fibres ; in other parts two were seen, one situated above the other ; and in some parts there were as many as six, all arranged close together in linear series ; some of them were seen to give off a nerve-tube at one extremity ; and once or twice the corpuscle was seen to be connected with two such, one passing towards the centre, the other in the direction of the peri phery.