COMPARATIVE ANATOMY OF THE STOMACH OF THE CETACEA - ONTOGENIC CHANGESINVOLVING GASTRIC PROPORTIONS MESENTERIES ARTERIES

This study discusses three aspects of the comparative anatomy of the s tomach in seven species of odontocete cetaceans: ontogenetic changes i n the proportions of four gastric regions, the lines of fixation of th e mesogastria to the stomach and the mode of branching of arteries tha t supply the organ. An interspecific comparison revealed a considerabl e postnatal increase in the relative volume of the forestomach, howeve r, in the harbour porpoise (Phocoena phocoena) there is a constant dec rease in the size of the forestomach during the time period when the t otal length of the embryo lies between 7% and 12% of the neonatal leng th. The forestomach, which is not differentiated in species of the cet acean family Ziphiidae (Mesoplodon densirostris was investigated here) , is completely differentiated on the ontogenetically left side of the stomach anlage, a situation that has only been found once - in the Br adypodidae or tree sloths - in terrestrial mammals. The branching mode of the arterial supply of the stomach showed only one synapomorphy be tween Stenella longirostris and Tursiops aduncus; where the A. gastric a sinistra is a branch of the A. hepatica communis In all other compar isons only symplesiomorphies could be discerned; between Mesoplodon de nsirostris and Grampus griseus in as many as three cases This relative ly high number of symplesiomorphies indicates that the gastric arteria l system in both species did not change significantly from the basic s ituation at the beginning of cetacean evolution.