9 



fibrous structure, formed mainly of a fold of peritoneum, is placed 

 across between the liver and the heart above, and the stomach and 

 spleen below. This fold is attached anteriorly and inferiorly to the 

 lower edge of the sternum, and it unites with the tendinous lamina of 

 the transversalis ; behind, this lamina is united to the diaphragm proper, 

 which we shall describe subsequently. This portion is not, however, a 

 complete septum. On removing the liver and heart, two large fibrous 

 laminae are exposed, covering the very large air sacs, which occupy a 

 large part of the thoracic cavity ; these laminse send in four septa on 

 either side, so as thus to subdivide the lateral portions of the cavity into 

 four compartments ; but the divisions are extremely loose and fibrous, 

 so that each compartment freely communicates with its neighbour. In 

 the centre of these compartments existed several peculiar oval bodies, 

 like lymphatic glands in appearance, and in structure composed of an 

 external rough, firm, fibro-cellular coating, with an internal yellowish- 

 brown matter of sebaceous consistence. These were about an inch long, 

 three-fourths broad, and one-fourth in thickness, and were arranged in a 

 line on each side, connected to the septa by ten or twelve threads, radiating 

 in all directions. Beneath these bodies and the air sacs, we find a true 

 muscular diaphragm, composed of a flat tendinous central lamina, and two 

 - lateral fleshy portions, concave in front and below, convex above and 

 behind ; it is attached on either side by five fleshy slips to the five lower 

 vertebral ribs along their margins ; the fibres run backwards and in- 

 wards to the tendons, and some pass a little upwards, and are about 2^ 

 inches in length. The kidney reaches to its lower border, and the spleen 

 lies on its inferior and posterior surface. The oesophagus pierces it in front, 

 and lies below it for a considerable distance ; the two lower muscular 

 fasciculi are separated from the upper by a large aperture, looking down- 

 wards, forwards, and outwards, which led to the air sac from the bronchial 

 tube. Two other large openings exist, one on either side of the 

 oesophageal orifice, which pass downwards and backwards ; and above, 

 and external to these, are two smaller holes, running in the same direc- 

 tion ; the two lower slips of muscular fibres are broad and flat, and the 

 upper are round and thick. The aorta passes through the lower border 

 of this true diaphragmatic structure, and on either side of it passes down 

 a tendinous slip or crus, to be attached to the sides of the bodies of the 

 lumbar vertebrae . 



The lungs are exposed on removing the diaphragm, and appear 

 placed at the upper and back part of the cavity of the thorax, filling the 

 spaces around the heads of the ribs ; into these organs pass the bronchial 

 tubes, one along the centre of each lung towards the base, the right 

 being more transverse and more curved than the left. These tubes are 

 membranous, and communicate with the air sacs by means of the open- 

 ings in the diaphragm ; all its branches come off in a regular series from 

 its posterior surface, and the trunk ends below by communicating with a 

 large air sac, which lies on either side of the back of the abdominal 

 cavity ; this latter is similar in structure to the thoracic series of air 

 cavities. The branches of the bronchus appear pinkish, and seem mus- 



R, T. A. PKOC— -VOL. IX. C 



