230 ON THE OBLIQTTB SBPTA IN THE PAflSEEINES. [Tel). 4, 



of that reptile are invested by a closely adherent membrane, which 

 has been thus described by Prof. Huxley ' : — " A fibrous expansion 

 extends from the vertebral column over the anterior face of the 

 stomach, the liver, and the dorsal and front aspect of the 

 pericardium, to the sternum and the parietes of the thorax, 

 separating the thoraco-abdominal space into a respiratory and a 

 cardio-abdominal cavity, and representing the oblique septum of 

 the bird." Both I " and Mr. G. W. Butler ^ have included in the 

 comparison which Prof. Huxley thus made the omentum of the 

 bird. But this does not interfere with the special likeness which 

 the Passerine shows to the Crocodile, in that the representative of 

 the oblique septum of other birds has not (as a rule) a ventral 

 attachment on each side to the sternum, but that it forms a 

 closely investing sheath to the liver-lobes ; but it is very doubtful 

 whether this resemblance is more than a superficial one. It is 

 agreed on all hands that the Passeres are a much, if not the most, 

 specialized group of birds, standing on the very topmost branch of 

 the avian tree. Among them, therefore, the retention of archaic 

 characters, though possible, would not be so likely as among some 

 other groups. Besides, the arrangement of the oblique septa in 

 them seems to be a secondary afiair on account of the fact that the 

 original (?) position of the attachment of those septa is indicated 

 by rudiments varying in degree of the portion of the septa which 

 was formerly inserted laterally and ventrally on to the sternum, 

 and the Book has these membranes complete. This may be in the 

 form of a much-fenestrated membrane, or there may be but a single 

 tag on each side near to the posterior margin of the sternum, or, as 

 in an example of Prosthemadera novce-zealandice, the attachment 

 may have been completely retained on one side. I should be dis- 

 posed, therefore, in spite of certain undeniable likenesses w hich 

 the Passerines show to the Crocodilia, to regard the relations of 

 the oblique septa in them as a modification of the more prevalent 

 disposition of those parts. 



In describing the septa of the somewhat aberrant Australian 

 Strutliidea, I called attention to the fact that the liver-lobes were 

 partly shut oif from the subomental space by membranous 

 partitions. The exact «ay in which these partitions are related to 

 the liver-lobes is, so far as my experience goes, unique among birds. 

 But there are other birds in which an arrangement of the same kind 

 exists ; but with certain differences. 



In several birds, for instance in Chrysotis guildingi, the left liver- 

 lobe is completely shut off from the subomental space by a vertical 

 transverse partition ; there is no corresponding partition on the 

 opposite side of the body. There are some birds in which, as in 

 Struihidea, there are partitions on both sides ; but in them the 

 partitions are quite complete and entirely shut off the liver-lobes 

 from the subomental space, not merely partially as in Strutliidea. 



» Loo. cit. p. 668. 



" " On the KeBpiratory Organs in certain Diving Birds," P. 55. S. 1888, p. 250. 



» " On the SubdiTieion of the Body-cavity in Lizards &o.," P. Z. S. 1889, p. 453. 



