| OCR Text |
Show 226 MR. F, E. BEDDARD ON THE [Feb. 4, called ' diaphragm ' (' diaphragme thoracoabdominal,' Sappey; ' diaphragmite thoracoabdominal,' Milne-Edwards) is a more or less aponeurotic fibrous membrane, continuous with the ventral edge of the median dorsal septum and suspended by it, like the roof of a tent, across the thoraco-abdominal cavity. In the middle line, this oblique septum slopes downward and forward to the dorsal and anterior face of the pericardium, with which its fibres become firmly connected on their way to their attachment to the sternum. From the median line, the two halves of the oblique septum slope laterally and ventrally until they attach themselves to the parietes of the abdomen behind, to those of the thorax more anteriorly, and to the margins of the sternum in front." In fact, if w e make a transverse section through a Duck or most other birds at the level of about the middle of the sternum, the appearances will be such as are diagram matically represented in the accompanying drawing (fig. 1, p. 227). Four membranes are there visible-the intestines being left out of consideration for the purposes of simplification, and as not germane to the structures at present under discussion. The first of these is the falciform ligament, which divides the lobes of the liver and is attached below to the middle line of the sternum. Then there are the oblique septum (O.S.), attached below to the sternum laterally, and above to the parietes; and finally the horizontal septum (A.S.), which floors the two cavities containing the liver-lobes. This arrangement, however, does not hold good for a number of Passerine birds; and it is possible-though I a m not yet in a position to make a definite statement about the matter-that the arrangement which I a m about to describe as characteristic of many Passerines will be found to be distinctive of the group. I commence with a somewhat detailed description of the oblique septa of a Crow (Corvus capellanus) (see fig. 2, p. 227). As I have dissected three examples of this bird, the following description will probably be found to be free from any record of abnormal conditions. The right lobe of the liver is considerably larger than the left, and extends some way beyond the margin of the sternum, in fact about as far as to the end of the posterior intermediate air-sac. It is separated from the liver-lobe of the left side as usual by a vertically directed septum, the umbilical or falciform ligament; this falciform ligament is attached to the ventral parietes for a distance of about an inch-from the posterior end of the sternum to a point rather in front of that which corresponds to the posterior margin of the hver. Anterior to the posterior edge of the sternum, the falciform ligament is not attached to that bone; it becomes fused with the two oblique septa, forming a roof over the liver-lobes in this region, which is separated by a wide interval from the internal surface of the sternum. The oblique septa are closely attached for a considerable distance to the liver-lobes, the adhesion being certainly not pathological. |
