411. CHAPTER V. THE PLEURA, THE MEDIASTINUM, AND THE PERICARDIUM.

HEISTER. "The pleura is a smooth, strong, tense membrane, adhering to the ribs and to the intercostal muscles, and surrounding the whole cavity of the thorax.

1. It consists of two sacs, each of which invests one side of the thorax, and each contains one of the two great lobes of the lungs: the conjunction of these sacs in the middle of the thorax produces the mediastinum.

2. It is composed of two very vascular lamellae.

3. It has numberless arteries, arising from the veins corresponding in name to the above arteries, but all of which terminate in the trunk of the vena azygos, and of the superior vena cava: nerves, from the thoracic vertebrae, and from the phrenic nerves; and lymphatics, which run to the thoracic duct.

4. Some writers attribute glands to the pleura, but without good reason. (Comp. Anat., n. 255.) All observations to this effect have been made upon diseased subjects, and derived from morbid conditions; but glands have never been shown in the pleura, so far as my knowledge extends, in healthy bodies. Hence I am induced to think, that the corpuscules taken for glands, are nothing more than tubercles, the products of disease, which have owed their origin to the stoppage of earthly or viscid matter in the delicate little arteries of these membranes, and c. (Ibid., not. 6.)

107. CHAPTER V. THE INTESTINES.

HEISTER. "The intestines are large and long membranous canals, reaching from the stomach to the anus. In these we are to observe their length, which is usually six times as much as the height of the man they belong to. Their wonderful circumvolutions. Their connection, by means of the mesentery, with the lumbar vertebrae. Their number; for though properly one, they are usually regarded as six. Three of these are called the small intestines; the first of which is the duodenum, so called from being about the length of twelve [duodecim] fingers. This intestine commences at the pylorus; it first ascends a little, then descends, and afterwards ascending again, it runs transversely towards the left kidney. At the distance of three or four fingers from the pylorus, it receives by a single prominent opening, the orifices of the ductus cholidochus and of the ductus pancreaticus, for taking up the bile and the pancreatic juice. Its coats are thicker, and its cavity larger, than those of the other small intestines. In its beginning, it has none of the valvulae conniventes Kerkringii, or rugae, but in its continuation it has great numbers, called by authors, juga. It has also great numbers of the glandular Brunneri, serving for the secretion of a thin fluid. Its arteries are from the coeliac, and its veins, like the rest of the intestinal veins, from the porta. The second of the small intestines is the jejunum; so called, because it is usually found empty, owing to the fluidity of the chyle, the greater stimulus of the bile in it, and the abundance of its lacteals. It is placed in the region above the umbilicus; and has a great many valvulae conniventes. It begins where the duodenum ends; and it terminates at the part where the valves are obliterated. Hence I have observed that its length varies in different subjects; ranging from thirteen to sixteen spans. It is generally shorter than the ileum. The third of the small intestines is the ileum; so called from being placed principally below the umbilicus, near the ossa ilei. Its length is various, sometimes scarcely fifteen spans, at others, more than twenty. It begins where the valvulae conniventes are no longer conspicuous, and ends where the large intestines begin: in which place it is inserted into the left side of the colon, in a remarkable manner, so as to form a valve, which is called the valvula coli, Bauhini. It has no valves of its own; hut its glands are in general more numerous towards its termination, than in any other part.