2. Intermediate non-vascular fold.] [Illustration: FIG. 582.--Human infant. Ileo-colic junction and caecum; ventral position of appendix. (Columbia University Museum, No. 693.)] In Fig. 581--a foetal preparation at term--the caecum is turned to the left, below and behind the terminal ileum. The non-vascular fold (2) is well developed as regards _length_ of _ileal_ attachment, but is very narrow and tense, passing between ileum and the proximal curve of the caecum behind the ileo-colic junction, where it merges with the dorsal vascular fold. The appendix takes a sudden turn caudad at this point and then continues up _ventrad_ to the ileo-colic junction, the proximal portion being kept firmly in contact with the dorsal and caudal circumference of the ileum by the tension of the non-vascular band. It is quite evident that this peculiar turn of the appendix is directly due to the confining influence of the non-vascular band--which passes from its ileal attachment almost directly dorsad to the point of fusion with the dorsal vascular fold, causing the sharp downward and forward turn of the proximal segment of the appendix. Similar cases with ventral position of the appendix are shown in Figs. 545 and 582. INDEX. Abdominal vein in Anure Amphibian, 158 in Reptilia, 167 in _Iguana_, 160 in Urodele Amphibian, 157 viscera of _Macacus rhesus_, 77 Abnormal positions of appendix, 277 Abomasum, 49 _Accipenser sturio_, biliary ducts in, 145 pyloric appendices in, 120 ileo-colic junction of, 212 Ailuroidea, ileo-colic junction of, 212 Alimentary canal of _Ammocoetes_, 42 of _Amphioxus_, 42 of _Belone_, 40 of _Chelydra_, 58 of Cyclostomata, 40, 42 derivation of epithelium, 30 of muscular and connective tissue, 30 differentiation from body-cavity, 21, 29 divisions of, 38 early developmental stages, 21, 29 mammalian embryonal stages, 40 of _Esox_, 40 of _Echelus conger_, 54 of _Necturus_, 40 of _Petromyzon_, 200 of _Proteus_, 40 primitive type, 40, 42 of _Pseudemys elegans_, 55 of _Rana_, 55 separation from yolk-sac, 22 tract of _Necturus maculatus_, 52 of _Tamandua_, 56 Allantois in Amniota, 36 arteries of, 63, 146 derivation from alimentary canal, 35 function of, 36 relation to placenta, 36 to primitive intestine, 24 to urinary bladder, 24 _Alligator mississippiensis_, ileo-colic junction of, 201 stomach of, 51 _Ammocoetes_, alimentary canal of, 42 pancreas in, 117 _Ammodytes_, pyloric appendix in, 120 Amnion, definition of, 36 Amniota, development of liver in, 143 Amphibia, development of pancreas, 115 folds of intestine in, 196 ileo-colic junction of, 201 Amphibians, biliary ducts in, 145 intestinal canal of, 191