1888.] 



VISCERAL ANATOMY OF BIRDS. 



257 



A difficulty in the way of this comparison is the relation of the 

 omentum to tlie 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 veutrally and dorsally, 

 and completely shut off a triangular segment of the coelom from that 

 portion of the coelom which contains the intestines ; the omentum 

 conies into contact with the oblique septum and even fuses with it, 

 but it is quite distiuct from it, iu the direction of its fibres, &c. It 



Diagrammatic transverse section through abdominal region of Emu, to 

 illustrate the oblique septum. 



a, oblique septum ; h, 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 Emu 

 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 

 veutral 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 he 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 



