| vitelline fistula | A fistula between the umbilicus and the terminal ileum along the course of a persistent vitelline cord. See: Meckel's diverticulum. (05 Mar 2000) |
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| vitelline layer of egg | <zoology> The membrane, usually of protein fibres, immediately outside the plasmalemma of the ovum and the earlier stages of the developing embryo. Its structure and composition vary in differing animal groups. (18 Nov 1997) |
| vitelline membrane | <cell biology> The plasma membrane of the egg. (12 Dec 1998) |
| Vitelline pole | <embryology> The vegetative pole of an ovum. (05 Mar 2000) |
| vitelline reservoir | In cestodes and trematodes, a common chamber receiving vitelline (yolk) material from the two vitelline ducts; the yolk material then passes into the ootype to surround the ovum with nutritive vitelline granules that are enclosed by a characteristically formed eggshell. Synonym: vitelline reservoir. (05 Mar 2000) |
| vitelline vein | <anatomy, vein> A vein returning blood from the yolk sac to the embryo. Synonym: vena vitellina. (05 Mar 2000) |
| vitelline vessels | See: vitelline artery, vitelline vein. (05 Mar 2000) |
| abdominal sac | The part of the embryonic celom that becomes the abdominal cavity. (05 Mar 2000) |
| air sac | <zoology> Thin-walled sacs or spaces which function as a part of the respiratory system in birds, fishes, insects, and mammals. The sacs are filled with air and connected with the air passages of the lungs; an air cell. Source: Websters Dictionary (04 Jul 1999) |
| allantoic sac | The dilated distal portion of the allantois; it forms part of the placenta in many mammals. (05 Mar 2000) |
| alveolar sac | Terminal dilation of the alveolar ducts that give rise to alveoli in the lung; a small air chamber in the pulmonary tissue from which the pulmonary alveoli project like bays and into which an alveolar duct opens; in birds, air-containing extensions of bronchi that connect with bone cavities. Synonym: sacculus alveolaris, air sac. (05 Mar 2000) |
| amniotic sac | <anatomy, obstetrics> Sac, enclosing the embryo of amniote vertebrates, that provides a fluid environment to prevent dehydration during development of land based animals. See: amnion. (18 Nov 1997) |
| anal sac | A vesicular cutaneous invagination opening by a duct on each side of the anal canal in carnivores (best developed in skunks, but absent in some bears, the raccoon, kinkajou, coati, and sea otter), each lying between the external and internal anal sphincter muscles, which aid in emptying the contents. The sac stores odouriferous scent markers produced by glands that line its wall or duct; frequently the sac becomes impacted in the dog or cat, requiring manual emptying. (05 Mar 2000) |
| aneurysmal sac | The dilated wall of an artery in a saccular aneurysm. (05 Mar 2000) |
| aortic sac | In mammalian embryos, the endothelially lined dilation just distal to the truncus arteriosus; it is the primordial vascular channel from which the aortic arches arise and is homologous to the ventral aorta of gill-bearing vertebrates. (05 Mar 2000) |