| allantoic sac | The dilated distal portion of the allantois; it forms part of the placenta in many mammals. (05 Mar 2000) |
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| 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) |
| rami laterales ramorum dorsalium nervorum cervicalium/thoracalium/lumbalium/sac | Lateral branch of dorsal primary rami of spinal nerves. See: lateral branches. (05 Mar 2000) |
| gestational sac | <radiology> Arises from blastocyst which implants into secretory endometrium surrounded by echogenic trophoblast sac size: 6th week = 17mm;, 8th week = 31 mm, fills chorionic cavity by 12th week visualization of gestational sac, relative to beta-hCG levels: transabdominal scan: greater than 1800 IU/l, transvaginal scan: less than 500 IU/l = 20%, 500-1000 IU/l = 80%, greater than 1000 IU/l = 100%, relative to menstrual age, transabdominal scan: earliest by 5.5 weeks (10-12mm), transvaginal scan: routinely seen by 5-5.5 weeks see: double decidual sac (12 Dec 1998) |
| gestation sac | The gestation sac is the fluid-filled sac in which the foetus develops, visible with an ultrasound exam. (09 Oct 1997) |
| vestibular blind sac | <anatomy> The lower extremity of the cochlear duct, occupying the cochlear recess in the vestibule. Synonym: caecum vestibulare, vestibular blind sac. (05 Mar 2000) |
| vitelline sac | <embryology, ornithology> One of the set of extra embryonic membranes, growing out from the gut over the yolk surface, in birds formed from the splanchnopleure, an outer layer of splanchnic mesoderm and an inner layer of endoderm. (18 Nov 1997) |
| pericardial sac | <anatomy> A tough fibrous membrane that envelops and protects the heart. (27 Sep 1997) |
| greater cul-de-sac | The portion of the stomach that lies above the cardiac notch. Synonym: fundus gastricus, fundus ventriculi, greater cul-de-sac. (05 Mar 2000) |
| Gruber's cul-de-sac | A lateral diverticulum in the suprasternal space beside the medial extremity of the clavicle behind the sternal attachment of the sternocleidomastoid muscle. (05 Mar 2000) |
| chorionic sac | 1. Protective membrane around the eggs of insects and fishes. 2. Extraembryonic membrane surrounding the embryo of amniote vertebrates. The outer epithelial layer of the chorion is derived from the tropoblast. (18 Nov 1997) |