DIGESTIVE SVSTEM 14! 
convolutions reveals their taxonomic value, and enables me to say 
that the Digestive System, taken in its entirety—that is to say, 
the crop, glandular and muscular stomach, liver, gall-bladder with 
its ducts, ceca, and the relative length and convolutions of the in- 
testinal canal—affords more diagnostic features than any other 
organic system—the osseous excepted. Moreover, it has the great 
advantage that through reference to the food we can in many cases 
account for the aberrant features of the digestive organs displayed 
by birds otherwise closely allied. So much cannot be said for char- 
acters furnished by PrERYLOSIS, and attempts to explain taxonomic- 
ally the more important differences observable in the MuscuLar 
System have hitherto been futile because of the complex problems 
involved. At any rate, we ought not to treat recent birds as if 
they were fossil and had left us nothing but their bones, unless, 
indeed, the specimens be skinned and all their other important char- 
acters thrown away. 
It is hoped therefore that a brief general account, condensed 
from a paper in the Zoological Proceedings for 1889 (pp. 303-316), 
of the chief types of intestinal structure in birds may here have 
interest, especially as, with the exception of Cuvier, British Ana- 
tomists only! have treated the subject, and since the days of 
Macgillivray, who alone attempted it systematically, this branch 
of Ornithotomy has been neglected, perhaps from the apparent but 
not real difficulty of studying these easily-putrefying organs. 
In a typical loop of the intestines of a bird we distinguish 
between a descending and an ascending branch ; both meet at the 
distal end or apex of the loop, and this forms its turning-point. 
The starting-point is the pylorus, the goal the cloaca. Each loop 
is either closed or open. It is closed when both the descending 
and the ascending branches are throughout the length of the loop 
closely bound together by an extension of the mesentery and its 
vessels. Of these vessels, as a rule, each principal loop receives 
one bigger branch from the middle mesenteric artery. A loop is 
open when its two branches are not closely connected by mesentery 
and vessels ; the mesentery is wider, and the two branches of the 
loop may receive another loop or intestinal fold between them, the 
latter then resting upon the mesentery of the former open loop. 
The duodenum is always a typically-closed loop. Its first or 
1 K. Home, The course of the intestine with the varieties in the form of the 
ceca in carnivorous, piscivorous, and granivorous birds, Phil. Trans, 1814. G. 
Cuvier, Legons @anatumie comparée, ed. 2, 1835. R. Owen, Todd’s Cyclopedia 
of Anatomy and Physiology, article ‘‘ Aves,” 1836. |W. Macgillivray, ‘‘ Obser- 
vations on the Digestive Organs of Birds,” Mag. Zool. and Bot. 1837. Occasional 
notes on the intestinal canal are extremely numerous, among others by Burton, 
Crisp, Duvernay, Forbes, Garrod, Jobert, Leuckart, L’ Herminier, Martin, Nitzsch, 
Pavesi, Perrin, and Yarrell. 
