ANTHELIX, in Anatomy, the inner Circuit of the Auricle; thus called from its opposition to the outer Circuit, called the Helix.
ANTICARDIUM, in Anatomy, etc., that Part of the Breast just against the Heart, commonly called the Pit of the Stomach. The Word is compounded of ἀντί, contra, against, and καρδία, Cor, Heart.
ANTIPERISTALTIC, in Anatomy, a Motion of the Intestines contrary to the Peristaltic Motion. See PERISTALTIC. The Peristaltic Motion is a Contraction of the Fibres of the Intestines from above, downwards; and the Antiperistaltic Motion is their Contraction from below, upwards. See INTESTINES. The Word is derived from the Greek ἀντί, against, περί, about, and στάλλω, that which has the Power of compressing. See VERMICULAR.
ANTITHENAR, in Anatomy, a Muscle of the Thumb whose Office is to draw it to the Fingers. It arises from the Bone of the Metacarpus that sustains the Fore-finger, and is inserted into the first Bone of the Thumb. See FINGER. ANTITHENAR is also the Name of a Muscle of the great Toe; which arising from the inferior part of the third Os Cuneiforme, and passing obliquely, is inserted into the inside of the Os Sesamoidea. See TOE. The Word is compounded of the Greek ἀντί, against; and θέναρ, as being Antagonist to the Thenar. See THENAR.
AORTA, in Anatomy, an Artery, which arises immediately out of the left Ventricle of the Heart; and is distributed thence through all Parts of the Body. See ARTERY and HEART. The Aorta is otherwise called the great Artery; as being the Trunk, out of which the other Arteries all spring; and the great Conduit or Canal whereby the Blood is conveyed throughout the Body. See BLOOD and CIRCULATION. The Word is formed of the Greek ἀορτή, which signifies a Vessel, Chest, etc. The Aorta is divided into two grand Trunks, called the Ascending and Descending Aorta, ascendens and descendens. See ASCENDING and DESCENDING. Ossifications, or Petrifications of the Coats of the Aorta at its rise from the Heart, are so frequent, that some think it a constant Case—Mr. Cooper, however, has an express Discourse to show that whenever such Ossification happens in Man, it is a Disease, and incommodes the Part in the due Execution of its Office. Of this he gives us several Instances; one, in which an Intermittence of Pulse was produced; in another, a Coldness of the Extremes with a Gangrene, etc. Phil. Transact. No. 299.
APOPHYSIS, in Anatomy, a Process or Protuberance of a Bone; being a part eminent or jutting out beyond the rest. See BONE, PROCESS, etc.
Such are the Eminences of the Vertebrae, the Scapula, Thigh-bone, etc. See VERTEBRA, SCAPULA, etc.
Apophyses Olfactoriae, are the Beginnings of the olfactory Nerves; as far as the Os Cribriforme, where they divide into little Fibres, which pass through those Bones, and spread themselves throughout the upper part of the Nose. See OLFACTORY NERVE, NOSE, etc.
Such are the Eminences of the Vertebrae, the Scapula, Thigh-bone, etc. See VERTEBRA, SCAPULA, etc.
Apophyses Olfactoriae, are the Beginnings of the olfactory Nerves; as far as the Os Cribriforme, where they divide into little Fibres, which pass through those Bones, and spread themselves throughout the upper part of the Nose. See OLFACTORY NERVE, NOSE, etc.
ARTERY,Arteria, in Anatomy, a hollow fistulous Canal, appointed to receive the Blood from the Ventricles of the Heart, and distribute it to all Parts of the Body, for the Maintenance of Heat and Life, and the Conveyance of the necessary Nutriment. See BLOOD, HEART, LIFE, &c. The Word is Greek, ἀρτηρία; which some imagine derived from ἀήρ, Aer, the Air, and τηρέω, tereo, to keep: But others who understand the Use of the Part better, derive it from ἄρτι τὴν ῥύσιν, because of its continual Throbbing or Beating. The Arteries are ordinarily composed of three Coats or Membranes. The first or outermost, nervous or tendinous; being a Thread of fine Blood Vessels with Nerves, for nourishing the other Coats. The second muscular, made up of circular, or rather spiral Fibres; of which there are more or fewer Strata, according to the Bigness of the Artery: These Fibres have a strong Elasticity, by which they contract themselves with Force, when the Paws by which they have been stretched out, ceases. The third and inmost Coat is a fine, dense, transparent Membrane, which keeps the Blood within its Channels, which otherwise upon the Dilatation an Artery, would easily separate the spiral Fibres from one another. As the Arteries grow smaller, these Coats grow thinner.
All the Arteriesare conical, i.e., begin with a Trunk, and growing less and narrower, end in Branches so minute, that they escape the Sight, unless assisted with Microscopes; by which, in the Tails of Tadpoles and very small Eels, the Extremities of the Arteries seem, by the swift uninterrupted Course of the Blood, to be inosculated or continued to the Originations of the Veins: Though by the Transparency of those Vessels, the actual Continuation be not visible. See Anastomosis, and Inosculation. The Coats of the Arteriesare of a very dense, close Contexture; by which means the Blood not being visible through them, they generally appear white. Add, that the Blood proceeding from a greater Capacity to a less, is thereby somewhat obstructed in its Passage; but being forced on by the Motion of the Heart, distends the Coats, and thereby occasions a salient Motion, called the Pulse.—By this Thickness and Whiteness of the Arteries, with the Pulsation observed therein, Arteries are distinguished from Veins. See VEIN. The Pulse of the Arteries,like that of the Heart, consists of two reciprocal Motions, a Systole or Contraction, and a Diastole or Dilatation: But they keep opposite Times; the Systole of the one answering to the Diastole of the other. See PULSE, SYSTOLE, and DIASTOLE. All the Arteries of the Body,we have observed, arise in two large Trunks; from the two Ventricles of the Heart. That from the right Ventricle, is called the Pulmonary Artery, serving to carry the Blood into the Lungs: That from the left, the Aorta, or great Artery; which, by its numerous Ramifications, furnishes all the rest of the Body, as far as the remotest Stages of Circulation. See CIRCULATION OF THE BLOOD. The Great Artery,after it leaves the Heart, divides into two large Trunks, called the ascending, or upper; and descending, or lower, Trunks. See AORTA. The ascending Trunk, or Aorta ascendens,conveys the Blood to the Head, and other upper Parts of the Body, and is subdivided into three Branches.— The first, the right Subclavian, whence arise the Carotid, Vertebral, Cervical, right Axillary, &c.—The second, is the left Carotid —The third, the left Subclavian; whence arise the left Cervical, Vertebral, and Axillary:—See each described in its proper Article, Subclavian, Carotid, Vertebral, Cervical, Axillary, &c. The descending Trunk, or Aorta descendens,carries the Blood to the Trunk, and the lower Parts of the Body. Out of this arise the Bronchial, Intercostals, Coeliac, Phrenic, Mesenteric, Emulgent, Spermatic, Iliac, Umbilical, Epigastric, Hypogastric, Crural, &c. with their several Ramifications.—See each in its Place. A Draught of the several Arteries, with their Divisions and Subdivisions, in their natural Order and Position, as taken from the Life; see in Plate Anatomy. Artery,is also applied to that fistulous Tube, composed of Cartilages and Membranes, which descends from the Mouth to the Lungs, for the Conveyance and Reconveyance of the Air, in Respiration. See Respiration and Lungs. : This is particularly called the Aspera Arteria, or Trachea, and popularly the Wind-pipe. See TRACHEA.
All the Arteriesare conical, i.e., begin with a Trunk, and growing less and narrower, end in Branches so minute, that they escape the Sight, unless assisted with Microscopes; by which, in the Tails of Tadpoles and very small Eels, the Extremities of the Arteries seem, by the swift uninterrupted Course of the Blood, to be inosculated or continued to the Originations of the Veins: Though by the Transparency of those Vessels, the actual Continuation be not visible. See Anastomosis, and Inosculation. The Coats of the Arteriesare of a very dense, close Contexture; by which means the Blood not being visible through them, they generally appear white. Add, that the Blood proceeding from a greater Capacity to a less, is thereby somewhat obstructed in its Passage; but being forced on by the Motion of the Heart, distends the Coats, and thereby occasions a salient Motion, called the Pulse.—By this Thickness and Whiteness of the Arteries, with the Pulsation observed therein, Arteries are distinguished from Veins. See VEIN. The Pulse of the Arteries,like that of the Heart, consists of two reciprocal Motions, a Systole or Contraction, and a Diastole or Dilatation: But they keep opposite Times; the Systole of the one answering to the Diastole of the other. See PULSE, SYSTOLE, and DIASTOLE. All the Arteries of the Body,we have observed, arise in two large Trunks; from the two Ventricles of the Heart. That from the right Ventricle, is called the Pulmonary Artery, serving to carry the Blood into the Lungs: That from the left, the Aorta, or great Artery; which, by its numerous Ramifications, furnishes all the rest of the Body, as far as the remotest Stages of Circulation. See CIRCULATION OF THE BLOOD. The Great Artery,after it leaves the Heart, divides into two large Trunks, called the ascending, or upper; and descending, or lower, Trunks. See AORTA. The ascending Trunk, or Aorta ascendens,conveys the Blood to the Head, and other upper Parts of the Body, and is subdivided into three Branches.— The first, the right Subclavian, whence arise the Carotid, Vertebral, Cervical, right Axillary, &c.—The second, is the left Carotid —The third, the left Subclavian; whence arise the left Cervical, Vertebral, and Axillary:—See each described in its proper Article, Subclavian, Carotid, Vertebral, Cervical, Axillary, &c. The descending Trunk, or Aorta descendens,carries the Blood to the Trunk, and the lower Parts of the Body. Out of this arise the Bronchial, Intercostals, Coeliac, Phrenic, Mesenteric, Emulgent, Spermatic, Iliac, Umbilical, Epigastric, Hypogastric, Crural, &c. with their several Ramifications.—See each in its Place. A Draught of the several Arteries, with their Divisions and Subdivisions, in their natural Order and Position, as taken from the Life; see in Plate Anatomy. Artery,is also applied to that fistulous Tube, composed of Cartilages and Membranes, which descends from the Mouth to the Lungs, for the Conveyance and Reconveyance of the Air, in Respiration. See Respiration and Lungs. : This is particularly called the Aspera Arteria, or Trachea, and popularly the Wind-pipe. See TRACHEA.