DEVELOPMENT. — the COW'S embryo of Si lines in length, the gangliated cord of the sympathetic in the thorax was observed, by Kiesselbach §, on either side of the spinal column in the form of a thick cord, presenting numerous inequalities. In the pig's embryo, eight lines in length, it presents, according to Valentin, the same aspect. It seems, at this period, to consist of a series of small ganglia placed almost in juxta-position to each other, the interval between the individual ganglia not being very distinct. In another embryo, measuring about thirteen lines in length, Bis choff found the gangliated chain distinctly formed, not only in the thoracic, but also in ti1C cervical region : the superior cervical ganglion presented the aspect of a small round nodule. In the cow's embryo, measuring about inches in length, I found the ganglia in the cerebral and spinal nerves, as well as those of the sympathetic, very distinct. The superior cervical ganglion of the sympathetic appeared as a small reddish grey mass, of an irregularly oval fortn, measuring about ul..,th of an inch in its longest diatneter, soft and breaking down readily. It was situated close to the pneumogastric, a narrow indistinct whitish line passing downwards from the lower part of the ganglion to that nerve. The lower cervical ganglion presented a more elongated form, and appeared to be prolonged into the first thoracic : the other thoracic ganglia appeared as minute greyish particles between the heads of the ribs, and measuring about -Ath of an inch in diameter. The ganglia in the lumbar and sacral regions pre sented in general a more elongated form, and were not so distinctly separated from one another : the connecting cord, especially in the sacral region, being short and thick, and looking as if it were a prolongation of the one ganglion into the other. None of the branches which are sent inwards from the sympathetic cord, nor the ganglia occurring upon them, could be accurately distinguished from the surrounding structures. As regards the ganglia occurring on the cerebral and spinal nerves, they were much more distinct than those of the sympathetic. The Gasserian
ganglion presented the form of a gm) ish white body, situated beneath the still soft and transparent dura mater : it measured about th of an inch in diameter, and presented an irregularly oval or triangular shape. It ap Peared to consist of several opaque portions, separated from one another by an intermediate more or less transparent substance, thus pre senting the appearance of being composed of several minute lobules. The ganglia on the posterior roots of the spinal nerves were also very distinct : they were arranged along the interior of the spinal canal, on each side, and rather anteriorly towards the bodies of the vertebrw, and concealed by the spinal cord. They presented an oblong or oval shape, mea sured about Ath of an inch in length and about 46th in breadth, and presented the same characters in regard to colour, &c., as the Gasserian ganglion.
In embryos from seven to eight inches in length, the superior cervical ganglion presents the same oval shape and reddish grey appear ance as before : it is larger, however, measuring about -,4th of an inch in its long diameter : it consists, as before, of a number of opaque round or oval portions : the intermediate sub stance exists in much smaller quantity. It is surrounded by a highly vascular sheath. Frorn its lower part the communicating cord is seen passing downwards for a short dis tance, when it is applied to the trunk of the pneumogastric. The cord presents a flat tened aspect, and is of a greyish red colour. The ganglia in other regions of the body, as well as the intermediate cord, are well fornaed, and much larger than before. The first sacral ganglion of either side appears to be amalgamated into a single ganglion situated in the medial line.
The splanchnic nerves and solar plexus, as well as its offsets, are distinctly visible. The rami cornmunicantes are also present ; so also the plexus on the abdominal aorta and epi gastric plexuses. The ganglia on the cerebral and spinal nerves present the same characters as before, with the exception that they are considerably larger.