1902-3.] Abdominal Viscera of Cercocebus fuliginosus, etc. 511 
the most caudal part of the caecum. The caecum is free, having 
neither a mesentery nor any other form of peritoneal reflection. 
There is no vermiform appendix. Owing to some degree of lateral 
flattening, the caecum may he described as having two surfaces and 
two curvatures. The greater curvature is mainly dorsal in position, 
but is also inclined slightly to the right. Traced from the 
commencement of the colon, it runs caudalwards for a little 
distance, then turns ventralwards and to the left to end at 
the apex. The lesser curvature is only very slightly concave. 
It is directed ventrally and looks a little towards the left. 
Measured from the apex to the entrance of the ileum, this 
curvature is only 30 mm. in length. The surfaces of the caecum 
are lateral and mesial. The former is in contact with the abdomi- 
nal wall, and looks somewhat ventralwards. The mesial surface is 
smaller in extent than the lateral, and is concave. It is applied to 
the last part of the colon (PI. I. fig. 2 and PI. II. fig. 3). 
On opening the caecum it is found that its walls are of con- 
siderable thickness. The ileo-caecal (or ileo-colic) orifice is in the 
form of a rounded opening surrounded by a thick and prominent 
circular fold of mucous membrane, which, in the hardened 
condition at any rate, does not give the impression that it could 
act as a very efficient valve. On a level with the opening there 
is a ridge ( Frcena of human anatomists) running across the dorsal 
part of the tube, but absent ventrally. Corresponding to the 
position of the fraena, there is a furrow on the surface ( frcenal 
furrow of Struthers (10)), which thus supplies a clear line of de- 
marcation between the caecum and the colon. 
Colon . — The colon is a tube of considerable length and of 
complicated arrangement. In none of the abdominal viscera is 
the value of hardening the body as a whole more clearly demon- 
strated than here. For, had the colon been of natural softness, its 
disposition could not have been so easily studied with any hope 
of arriving at a reliable conclusion. Since it is disposed in a 
manner very similar to the condition found in man, the first part 
may be called the ascending colon , though this is not a strictly 
accurate term as applied to an organ in a pronograde animal. 
It runs straight cephalwards for a short distance, and then makes 
a wide curve in a ventral direction and to the left, to terminate in 
