THE STOMACH 



391 



large as the abomasum; in ten or twelve weeks this ratio is reversed. During 

 this period the omasum appears to be contracted and f unctionless. At four months 

 the rumen and reticulum together are about four times as large as the omasum 

 and abomasum together. At about one and one-half years the omasum equals 

 (or nearly so) the abomasum in capacity. The four divisions have now reached 

 their definitive relative capacities, the rumen constituting about 80 per cent., the 

 reticulum 5 per cent., the omasum 7 or 8 per cent., and the abomasum 8 or 7 per 

 cent, of the total amount. 



Exterior and Relations 

 The rumen occupies almost all of the left half of the abdominal cavity, and 

 extends considerably over the median plane ventrally and in its middle. It is some- 

 what compressed laterally, and may l^e described as having two surfaces, two curva- 

 tures or borders, and two extremities. The parietal (or left) surface (Facies 

 parictalis) is convex and is related to the diaphragm, spleen, and the left wall of 

 the abdomen. It extends from the lower part of the seventh intercostal space 



Fig. 288. — Projection of Viscera of Cow on Body-wall, Left Side. 

 Oes., GSsophagus; Ret., reticulum; b.s., anterior blind sac; b.s.', b.s"., posterior blind sacs of rumen; O, 

 ovary. The left kidney, concealed by the dorsal sac of the rumen, is indicated by dotted line. The median 

 line of the diaphragm is dotted. 



almost to the pelvis. The visceral (or right) surface (Facies visceralis) is somewhat 

 irregular, and is related chiefly to the omasum and al^omasum, the intestine, the 

 liver, pancreas, kidneys, the uterus in the female, and the posterior aorta and vena 

 cava. The dorsal curvature (Curvatura dorsalis) is convex, following the curve 

 formed by the diaphragm and sublumbar muscles. It is firmly attached to the 

 left portion of the crura of the diaphragm and the sublumbar muscles by peri- 

 toneum and connective tissue. The ventral curvature is also convex and lies on 

 the floor of the abdomen. The surfaces are marked Ijy the right and left longitudi- 

 nal furrows (Sulci longitudinales), which indicate externally the division of the 

 rumen into dorsal and ventral sacs.^ The reticular (or anterior) extremity (Ex- 

 tremitas reticularis) is divided ventrally by a transverse groove (Sulcus ruminis 

 cranialis) into two sacs. The dorsal sac is the longer of the two, and curves ven- 

 trally over the round, blind end of the ventral sac. The former only is continuous 



' It has been customary to term the sacs left and riglit respectively, but these do not repre- 

 sent the relations as they exist in situ and as they are presented on frozen sections. 



