OCR Text |
Show 1888.] VISCERAL ANATOMY OF BIRDS. 257 A difficulty in the way of this comparison is the relation of the omentum to the oblique septa in many birds ; the oblique septa pass from the hinder part of the abdominal cavity arising from, or near, the pubis ; they are attached to the parietes ventrally and dorsally, and completely shut off a triangular segment of the coelom from that portion of the ccelom which contains the intestines; the omentum comes into contact with the oblique septum and even fuses with it, but it is quite distinct from it, in the direction of its fibres, &c. It Fig. 2. I Diagrammatic transverse section through abdominal region of E m u , to illustrate the oblique septum. a, oblique septum; b, umbilical ligament. might appear therefore at first sight as if the omentum was a structure peculiar to birds and that the whole of the "fibrous expansion" of the Crocodile represented the oblique septa, the only difference being that in the birds the two halves had shrunk away from each other towards the lateral parietes. The relation of the oblique septa to the omentum in the E mu is rather different from that of many birds and enables this difficulty to be surmounted. The oblique septa pass back to the extremity of the abdominal cavity, but posteriorly they are not attached to the ventral parietes; the oblique septum has thus a free ventral edge for a considerable length; the omentum is attached to it apparently as in other birds, but on stretching the oblique septum the free edge is seen to be double and really to be produced by an upward fold ; at this point the strong interlacing tendinous fibres of the oblique septum disappear and the membrane passes without any break into the omentum. If this membrane is sufficiently stretched |