Non-vascular ileo-caecal folds, 262 Nucleolus, 19 Nucleus, 19 Nutritive yolk, 19 _Nycticebus tardigradus_, ileo-colic junction and caecum of, 213 spiral colon of, 234 _Nyctipithecus commersonii_, ileo-colic junction and caecum of, 214 OEsophageal gutter of ruminants, 49 OEsophageo-gastric junction, 45 Omega loop, development of, 77 Omental bursa, 107 early stages of, 104 Omentum, great, 107 layers of, 107 peritoneal adhesions in adult, 131 relation of, to transverse colon, transverse colon and duodenum, 129 lesser, as part of ventral mesogastrium, 165 divisions of, 172 in _Macacus_, 176 Omnivora, gastric diverticula of, 48 Omphalo-mesenteric arteries, 64, 146 artery, persistence of rudiments of, 65 duct, 22 veins, 146 Ophidia, intestinal villi of, 195 liver in, 144 stomach of, 44, 46 Oral pouches, 48 _Ornithorhynchus anatinus_, ileo-colic junction and caecum of, 204 _Orycteropus_, ileo-colic junction and caecum of, 208 _Oryx leucoryx_, ileo-colic junction and caecum of, 210 spiral colon of, 233 _Otolicnus crassicaudatus_, ileo-colic junction and caecum of, 213 _Ovis aries_, spiral colon of, 233 Ovum, structure of, 19 Owl, stomach of, 50 Pancreas, adhesion of, 67 adhesion of mesoduodenal segment, 123 in _Ammocoetes_, 117 in Chelydra, 117 comparative anatomy of, 116 concealed, of Teleosts, 117 derivation of, 34 development of, in Amphibia, 115 of, in cat, 115 of, in chick, 115 of, in fish, 115 of, in lower vertebrates, 115 of, in man, 111, 115 of, in sheep, 115 in foetal pig, 123 function of, 195 in _Myxinoids_, 117 peritoneal relations, 122 vascular and visceral relations of adult, 125 in _Protopterus_, 117 relation to dorsal mesogastrium, 123 to mesoduodenum, 122 to omental bursa, 123 in Selachians, 116 Pancreatic ducts in Mammalia, 117 normal arrangement, 113 secondary, 111 variations, 114 Pancreatico-gastric folds in man, 187 in _Nasua rufa_, 181 Papilla Vateri, 114 _Paradoxurus typus_, ileo-colic junction of, 212 _Paralichthys_, pyloric appendices in, 120 Parietal mesoderm, 21 peritoneum, definition of, 32 _Pelamys_, pyloric appendices in, 120 Pelvic vein in Anure Amphibian, 158 _Perameles nasuta_, ileo-colic junction and caecum of, 206 _Perca_, pyloric appendices in, 120 Perennibranchiates, stomach of, 44, 46 Perissodactyla, ileo-colic junction of, 210 Peritoneal cavity, lesser, summary and development of structure, 180 relations and position of appendix, 250 of appendix, variations of, 258 sac, lesser, of cat, 128