of Indian rivers. The neck, though long and slender, must have been rather stifl, because the bodies of the vertebrae are nearly flat-ended, while they bear short ribs: it could not have been bent in the swan-fashion represented in many restorations. The other vertebrae are similarly almost flat-ended and irmly united, but there is no sacrum. The ribs are single-headed, and in the middle of the trunk, between the supports of the paired limbs, they meet a dense plastron of abdominal ribs. The short tail is straight and rapidly tapering, but one specimen in Berlin suggests that it was provided with a rhomboidal flap of skin in a vertical plane. The bones in the ventral wallof the body which support the paired limbs are remarkably expanded, and those of the pectoral arch have often been compared with the corresponding bones of turtles. The limbs are elongated paddles, with five complete digits, of which the constituent bones (phalanges) are unusually numerous. The only traces of skin hitherto discovered suggest that it was smooth. The reptile must have been almost exclusively aquatic, feeding on cuttlefishes, fishes and other animal prey. It propelled itself chiefly by the paddles, scarcely by the tail.
The typical species is Plesiosaurus dolichodeirus, from the Lower Lias of Lyme Regis, which attains a length of about three metres. Other species from the same formation seem to have measured five to six metres in length, and there are species of allied genera from the Upper Lias which are probably still larger. A fine large skeleton from the Upper Lias of Württemberg, now in the Berlin Museum, is named Plesiosaurus guilelmi-imperatoris (see figure above). Cryptoclidus, known by complete skeletons from the Oxford Clay of Peterborough, differs very little from Plesiosaurus. The Cretaceous Cimoliosaurus, found in North and South America, Europe and New Zealand, is also very similar. The fossilized contents of the stomach in some of the later Plesiosaurs show that these reptiles swallowed stones for digestive purposes like the existing crocodiles.
References.—R. Owen, Fossil Reptilia of the Lassie Formations, pt. iii. (Monogr. Palaeont. Soc., 1865); W. Dames, paper in Abhandl. k. preuss. Akad. Wiss. (1895), p. 1. (A. S. Wo.)
PLEURISY, or Pleuritis (Gr. πλεῦρα=ribs), inflammation
of the pleura, caused by invasion by certain specific microorganisms.
(See Respiratory System: Pathology.) Secondary
pleurisies may occur from extension of inflammation from
neighbouring organs.
The morbid changes which the pleura undergoes when inflamed consist of three chief conditions or stages of progress. (1) Inflammatory congestion and infiltration of the pleura, which may spread to the tissues of the lung on the one hand, and to those of the chest wall on the other. (2) Exudation of lymph on the pleural surfaces. This lymph is of variable consistence, sometimes composed of thin and easily separated pellicles, or of extensive thick masses or strata, or again showing itself in the form of a tough membrane. It is of greyish-yellow colour, and microscopically consists mainly of coagulated fibrin along with epithelial cells and red and white blood corpuscles. Its presence causes roughening of the two pleural surfaces, which, slightly separated in health, may now be brought into contact by bands of lymph extending between them. These bands may break up or may become organized by the development of new blood vessels, and adhering permanently may obliterate throughout a greater or less space the pleural sac, and interfere to some extent with the free play of the lungs. (3) Effusion of fluid into the pleural cavity. This fluid may vary in its characters.
The chief varieties of pleurisy are classified according to the variety of the effusion, should effusion take place. (1) Some pleurisies do not reach the stage of effusion, the inflammation terminating in the exudation of lymph. This is termed dry pleurisy. (2) Fibrinous or plastic pleurisy. In this variety the pleura is covered by a thick layer of granular, fibrinous material. Fibrinous pleurisy is usually secondary to acute diseases of the lung such as pneumonia, cancer, abscess or tuberculosis (3) Sero-fibrinous pleurisy. This is the most common variety, and produces the condition commonly known as pleurisy with effusion. The amount may vary from an almost inappreciable quantity to a gallon or more. When large in quantity it may fill to distension the pleural sac, bulge out the thoracic wall externally, and compress the lung, which may in such cases have all its air displaced and be reduced to a mere fraction of its natural bulk. Other organs, such as the heart and liver, may in consequence of the presence of the fluid be shifted away from their normal position. In favourable cases the fluid is absorbed more or less completely and the pleural surfaces again may unite by adhesions; or, all traces of inflammatory products having disappeared, the pleura may be restored to its normal condition. When the fluid is not speedily absorbed it may remain long in the cavity and compress the lung to such a degree as to render it incapable of re-expansion as the effusion passes slowly away. The consequence is that the chest wall falls in, the ribs become approximated, the shoulder is lowered, the spine becomes curved and internal organs permanently displaced, while the affected side scarcely moves in respiration. Sometimes the unabsorbed fluid becomes purulent, and an empyema is the result.
The symptoms of pleurisy vary; the onset is sometimes obscure but usually well marked. It may be ushered in by rigors, fever and a sharp pain in the side, especially on breathing. Pain is felt in the side or breast, of a severe cutting character, referred usually to the neighbourhood of the nipple, but it may be also at some distance from the affected part, such as through the middle of the body or in the abdominal or iliac regions. On auscultation the physician recognizes sooner or later “ friction,” a superficial rough rubbing sound, occurring only with the respiratory acts and ceasing when the breath is held. It is due to the coming together during respiration of the two pleural surfaces which are roughened by the exuded lymph. The pain is greatest at the outset, and tends to abate as the effusion takes place. A dry cough is almost always present, which is particularly distressing owing to the increased pain the effort excites. At the outset there may be dyspnoea, due to fever and pain; later it may result from compression of the lung.
On physical examination of the chest the following are among the chief points observed: (1) On inspection there is more or less bulging of the side affected, should effusion be present, obliteration of the intercostal spaces, and sometimes elevation of the shoulder. (2) On palpation with the hand applied to the side there is diminished expansion of one-half of the thorax, and the normal vocal fremitus is abolished. Should the effusion be on the right side and copious, the liver may be felt to have been pushed downwards, and the heart somewhat displaced to the left; while if the effusion be on the left side the heart is displaced to the right. (3) On percussion there is absolute dullness over the seat of the effusion. If the fluid does not fill the pleural sac the floating lung may yield a hyper-resonant note. (4) On auscultation the natural breath sound is inaudible over the effusion. Should the latter be only partial the breathing is clear and somewhat harsh, with or without friction, and the voice sound is a ego phonic. Posteriorly there may be heard tubular breathing with a ego phony. These various physical signs render it impossible to mistake the disease for other maladies the symptoms of which may bear a resemblance to it, such as pleurodynia.
The absorption or removal of the fluid is marked by the disappearance or diminution of the above-mentioned physical signs, except that of percussion dullness, which may last a long time, and is probably due in part to the thickened pleura. Friction may again be heard as the fluid passes away and the two pleural surfaces come together. The displaced organs are restored to their position, and the compressed lung re-expanded. Frequently this expansion is only partial.
In most instances the termination is favourable, the acute symptoms subsiding and the fluid (if not drawn off) becoming absorbed, sometimes after re accumulation. On the other hand it may remain long without undergoing much change, and thus \a condition of chronic pleurisy becomes established.
Pleurisy may exist in a latent form, the patient going about for weeks with a large accumulation of fluid in his thorax. the
