1-laving premised these general iemarks on the glan dular system, we shall now examine such of the secret ing glands and organs of excretion as we have not yet described, or svhieh do not more properly belong to the succeeding chapters. We shall begin with the salivary glands and the pancreas, all of which we shall find to be intimately connected in their structure, and in the na ture of the fluid which they secrete.
Of the Salirara Glands and Pancreas.
The salivary glands consist, as we have seen, of the two parotids, the two sub-maxillary glands and the sub lingual glands. The situation of these is sufficiently described in the table. With respect to structure, they all pretty nearly resemble each other. Tney are all of a grayish colour, of a pretty firm texture, and composed of several very apparent separate lobes, connected by cellular substance, which gives to their peripheral sur face a very thin and delicate coat. Besides this thin coat from the cellular membrane, they are furnished with another peripheral membrane, derived from the cellular substance of the neighbouring organs, and this is attached to them more loosely. They all receive their blood-vessels by numerous ramifications, and they have all excretory ducts opening into the cavity of the mouth. They differ from each other in size and form. The parotid glands are the largest, and of a long irre gular shape; the sub-maxillary glands are smaller and rounder than the parotids, and the sub-lingual glands are the least, of an oval form and flattened. They differ also in their excretory ducts. Those of the parotid glands arc of a large size, and have very thick coats, though their internal diameter is very small. They pass from the atlantal and inial part of the glands, in a transverse direction over the tendons of the massete• muscles, whence they descend a little, and open into the mouth, through a perforation in the buccinator mus cles opposite to the second or third grinder of the upper jaw. The excretory ducts of the sub-maxillary glands are longer than those of the parotids, but their coats are thinner. They pass between the mylo-hyoidei and grnio.. glossa muscles, and open into the mouth behind the cut ting teeth of the lower jaw, by two small papillary ori fices. The excretory ducts of the sub-lingual glands are not formed into a single trunk, like those of the two former pairs, but they open by several orifices arranged in a line along the gums, a little on the outside of the frenum of the tongue. The arteries that supply the
parotid glands conic from the temporal arteries; those of the sub-maxillary from the facial, and those of the sublingual teem the lingual arteries. All their veins terminate in the external jugulars. The nerves are chiefly from branches of the inferior maxillary Ilene, and from the fiord° Jura of the seventh pair.
The salivary glands in new-born infants arc propor tionally smaller than at any future period; their action is very trifling, and for the first few weeks, the secre tion of saliva is but small. This secretion is, howe er, remarkably increased during dentition. The parotid gland in infants is of a yellowish colour, and their saliva is often remarkable for giving a yellow tinge to linen.
These glands, especially the parotid, sympathise in particular cases, with other glandular organs, especially with the testes in men, and the breasts in women, as appears from the curious phenomena that take place in that inflammatory affection of the parotid, called by phy sicians cynanche parotidea, and in common language the mumps.
Many of our later anatomists and physiologists have remarked a striking similarity, both in structure and functions, between the pancreas and the salivary glands; but scarcely any anatomical writers, if we except M. Roux, the writer of the 5th volume of Bichat's .1natomi• Descriptive, have described them in the same part of their systems.
The pancreas, or, as it is popularly termed, the swret bread, is of a long flat form, and is situated transversely within a doubling of the inesocolon, extending towards the left to the spleen, and towards the right to the first curvature of the duodenum, to the side of which it is attached by a small oblong process, commonly called the head of the pancreas. This process was, by Wins low, its discoverer, called the lesser pancreas. The pancreas may be considered as the largest of the sali vary glands, and in its general shape, has been said to resemble a clog's tongue. Its broad surfaces look ster nal and dorsad, and its edges nearly atlantad and sacrad. It passes over the aorta, the vena cava, and part of the splenic vessels, to all of which it is attached by cellular substance, by which it is also connected with the verte bra. Sternad it is enveloped by two layers from the mot of the mcsocolon.