| primitive pit | The depression in the primitive node that serves to connect the notochordal canal with the surface ectoderm and the yolk sac. These connections are referred to as the neurenteric canal. (05 Mar 2000) |
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| primitive reticular cell | A cell with processes making contact with those of other similar cell's to form a cellular network; along with the network of reticular fibres, the reticular cell's form the stroma of bone marrow and lymphatic tissues. (05 Mar 2000) |
| primitive ridge | One of the paired ridge's on either side of the primitive groove. (05 Mar 2000) |
| primitive streak | An ectodermal ridge in the midline at the caudal end of the embryonic disk from which arises the intraembryonic mesoderm; achieved by inward and then lateral migration of cells; in human embryos, it appears on day 15 and gives a cephalocaudal axis to the developing embryo. Synonym: germinal streak. (05 Mar 2000) |
| neuroectodermal tumour, primitive | A malignant brain tumour sharing common features and biologic properties with medulloblastoma. Some pathologists and clinicians use the terms interchangeably: they both can disseminate throughout the nervous system and, in some cases, systemically. most lesions arise from the posterior fossa in children under five years of age. The tumour often produces hydrocephalus and symptoms of increased intracranial pressure. Papilledema is often present. (12 Dec 1998) |
| anterior basal segment | Anterior basal segment of inferior lobe of right and left lung; lies between middle lobe and diaphragm. Synonym: segmentum basale anterius. (05 Mar 2000) |
| anterior eye segment | That part of the eyeball anterior to the lens. (12 Dec 1998) |
| anterior inferior segment | Anterior inferior segment of kidney. Synonym: segmentum anterius inferius. (05 Mar 2000) |
| anterior ocular segment | That portion of the eye comprising the cornea, iris, lens, and their associated chambers and adnexa. (05 Mar 2000) |
| anterior segment | A delimited part or section of an organ or other structure which lies in front of or ventral to the other similar parts or sections. 1) segmentum anterius (hepar); the anterior segment of the right lobe of the liver. 2) segmentum anterius (pulmo dexter et sinister); [S 3]; the anterior segment of the superior lobe of the right and left lungs. 3) anterior segment of the eye; the intraocular segment of the eyeball occupied by the aqueous which lies in front of, and is separated from the vitreous-filled posterior segment by, the lens and zonule; it is subdivided by the iris into anterior and posterior chambers. Synonym: segmentum anterius. (05 Mar 2000) |
| anterior superior segment | Anterior superior segment of kidney. Synonym: segmentum anterius superius. (05 Mar 2000) |
| apical segment | Apical segment of the superior lobe of the right lung, apical segment of the inferior lobe of the right and left lungs. Synonym: segmentum superius. Synonym: segmentum superius, segmentum apicale, superior segment. (05 Mar 2000) |
| apicoposterior segment | Apicoposterior segment of superior lobe of left lung, composed of two segments and wedged between the anterior segment of the upper lobe and the oblique fissure. Synonym: segmentum apicoposterius. (05 Mar 2000) |
| artery of anterior inferior segment of kidney | Origin, anterior branch of renal. See: segmental arteries of kidney. Synonym: arteria segmenti anterioris inferioris renis, artery of anterior {inferior segment of kidney}. (05 Mar 2000) |
| artery of anterior superior segment of kidney | Origin, anterior branch of renal. See: segmental arteries of kidney. Synonym: arteria segmenti anterioris superioris renis, artery of anterior {superior segment of kidney}. (05 Mar 2000) |