In embryos measuring seventeen or eighteen inches in length, not only can the parts which have been already mentioned be distinctly seen, but also most of the peripherical branches of the sympathetic. The superior cervical ganglion presents, as before, a more or less oval shape, and measures about ith of an inch in its long diameter. It has still the appearance of being composed of a number of round or oval opaque greyish-white masses : there appears, however, to be very little of the intermediate transparent substance present. Its sheath is very vascular, and numerous vessels also pass into the interior of the ganglion between its lobules : it is possessed of considerable con sistence. Its branches of communication with the different nerves are also distinctly seen : they have a more or less greyish red ap pearance. The lower cervical ganglion pre sents an irregularly oblong shape, about ith of an inch in length and TI6th of an inch in thickness, and still has the appearance of being prolonged downwards into the first thoracic ganglion. The thoracic ganglia are much smaller, measuring about of an inch ; and are more or less triangular in shape, present ing the lobulated aspect above described. The connecting cord between the different ganglia has a reddish grey colour, is flattened, mea suring about Ath of an inch in breadth, and presents the appearance of consisting of dis tinct bundles of fibres. A portion of these can be traced over the surface of the ganglia, others appear to sink into them, while a con siderable number can be traced into the rami communicantes. The latter are very distinct; some of them in the thoracic region appear to be abnost as thick as the cord of the sympa thetic itself, and ail of them present the same greyish red appearance. On turning ininards to the sympathetic, many of their fibres are seen to be prolonged into the main cord of the sympathetic, and merely run along the sides of the corresponding ganglia : these pass both upwards towards the head, and down wards in the direction of the pelvis. They join the spinal nerves at the point where the anterior and posterior roots become united into a common trunk. By far the greater portion of the fibres in the rami communi cantes run inwards towards the spinal cord.
The splanchnic nerve, which is about ith of a line in thickness, has a whiter aspect than the main cord of the sympathetic.
The nerves on the surface of the heart are very numerous and distinct, presentirw the same arrangement as has been ahead; de scribed. The cceliac and epigastric plexuses are also large ; the latter containing several ganglia. There are also several small ganglia in the plexus upon the abdominal aorta.
The ganglia on the cerebral and spinal nerves present much the same appearance as those in the animal after birth, only they are softer and have a redder colour.
As regards the development of the sympa thetic in the human subject, it would appear from the observations of Lobstein#, that in the embryo of the 14th week, about three inches in length, the main cord of the nerve was very apparent. In the chest it constituted a thick cord of a red colour, the ganglia being closely approximated towards one another. The superior cervical ganglion was very well formed, and about two lines in length, and half a line in thickness. The great splanchnic nerve existed as a very delicate filament : the semi lunar ganglia were almost imperceptible.
In an embryo male, about five months, old and measuring six inches in length, Lobstein found the trunk of the sympathetic very dis tinctly developed. It constituted an uninter rupted cord extending from the base of the cranium to the pelvis. The superior cervical ganglion was rounder than in the adult : it was three lines in length, and about half a line in thickness. The greater splanchnic nerve was very distinct, but very delicate, and arose by three roots. The semilunar ganglia were small, indistinct, and measured only about half a line in their greatest diameter. They were adherent to the supra-renal cap sule and to the vessels. The thoracic ganglia, with the exception or the first, constituted little enlargements about half a line thick. According to Kiesselbach, the solar ganglia do not make their appearance until about the ith month. At the 5th month, he found the ophthalmic and submaxillary ganglia formed ; and about theSth month, the spheno-palatine ganglion appears ; and in the 5th month, ac cording to the same author, the communi cating branches between the sympatlictic and cerebro-spinal system appear.
In the fcetus of eight months, the superior cervical ganglion, according to Lobstein, mea sures about five lines in length, and a line and a half in breadth. The greater splanchnic nerve is very distinct, but very fine, and tenninates in an imperfect semi-lunar ganglion.
In the fcetus, at the full period, the superior cervical ganglion, according to Lobstein, mea sures about SI lines in length, and furnishes four filaments to the branches of the external carotid, while a fifth is lost on the crico thyroid artery. The thoracic ganglia are well formed, and measure about a line in diameter, with the exception of the first, which mea sures about 5 lines. They are of a red colour ; and nearly all of them receive two branches from the intercostal nerves. The trunk or the sympathetic is very thick ; the interval between the ganglia is about -1-th of a line. The lumbar ganglia are very apparent. The semilunar ganglia are of small size com pared with the other ganglia. Lobstein failed to find the coccygeal ganglion in the child immediately after birth; according to Kiessel bach, on the other hand, it appears about the fifth month.
With respect to the minute structure of the ganglia and nerves in the fcetus, the Gas serian ganglion in the fcetal calf, 14 inch in length, consists of the followira, elements : 1st, bodies measuring from the Wz-ath to the sy" 35-uth of an inch in diameter, and presenting a slightly granular surface (most of them are round ; others have more or less an oval shape); 2nd, distinct cells measuring from the -1-010-6th to the -thwth of an inch in dia meter they contain a finely molecular fluid, and also a nucleus. The latter, which is fre quently situated towards one side of the cell, is round and granular, and generally contains a nucleolus. With the exception of their smaller size, they resemble ordinary ganglionic cor puscles. The nerves in the ganglion present the aspect of flattened bands of blastema, consisting ahnost entirely of corpuscles re sembling those first described, arranged close together in linear series in a somewhat gra nular matrix. They vary in breadth consi derably. The ganglia on the posterior roots of the spinal nerves present the same struc ture.