220 



ARTERY. 



brachi&us externus, arises by an acute point 

 from the internal ridge of the os humeri, be- 

 ginning immediately below the insertion of 

 the teres major; it also arises from the internal 

 ridge as far down as the internal condyle, from 

 the surface of the humerus behind this ridge, 

 and from the posterior surface of the internal in- 

 termuscular ligament. The three heads unite 

 above the middle of the os humeri, and cover the 

 whole of the back part of that bone ; they form 

 a thick broad tendon, which is inserted into 

 the rough surface on the superior part of the 

 olecranon process of the ulna, adhering closely 

 to the ligamentous fibres covering the posterior 

 surface of the synovial membrane of the 

 elbow-joint ; the lowest fibres of the second 

 and third heads of this muscle, which arise 

 from the back of the condyles, run nearly 

 horizontally into the tendon. 



The triceps is covered posteriorly by the 

 teres minor, deltoid, fascia of the arm and in- 

 teguments ; in front it is in contact with the 

 posterior surface of the humerus, the inter- 

 muscular ligaments, and the back part of the 

 capsule of the elbow-joint. This muscle ex- 

 tends the elbow ; when the long head contracts, 

 it draws the scapula towards the humerus, 

 and, if the scapula be fixed, it draws the 

 humerus backwards. 



For BIBLIOGRAPHY, see MUSCLE, and ANATOMY 

 (INTRODUCTION). 



(J. Hart.) 



ARTERY, (normal anatomy): aT?ia, ano 

 Toy TOK aepa, TVJPSIV, ab aere servando. 1'r. ar- 

 tere. Germ. Pulsader, Schlagader. Ital. arteria. 

 The arteries are the vessels which carry the 

 blood from the heart, and distribute that fluid 

 throughout the body. The trachea was ori- 

 ginally called artery from the circumstance of 

 its containing the air which it transmits to the 

 lungs. The term artery was exclusively ap- 

 plied to the trachea by Hippocrates and his 

 cotemporaries, by whom the vessels now called 

 arteries were described as pulsating veins. 

 Aristotle restricted the term artery to the tra- 

 chea, and described the aorta as the lesser 

 vein. We find these vessels called arteries 

 in the writings of Aretaus, Pliny, and Hero- 

 philus, probably on account of the adoption of 

 the opinion of Erasistratus, who taught that they 

 contained a vapour or spirit. The vessels now 

 known as arteries, however, were more dis- 

 tinctly so designated by Galen, who affirmed 

 that they were full of blood, and described the 

 arteries and veins as forming each a tree, whose 

 roots implanted in the lungs, and whose 

 branches distributed through the body, were 

 united by a common trunk in the heart. 



There are two great arterial trunks the 

 aorta, which arises from the left ventricle of 

 the heart, and the pulmonary artery, which 

 arises from the right ventricle of that organ. 

 Each of these vessels has an origin, a trunk, 

 and branches, which divide and subdivide in 

 an arborescent form, until they are reduced in 

 size to the most delicate degree of minuteness, 

 terminating in the capillary vessels, which can 

 be traced entering into all structures except 

 cartilage, hairs, and epidermoid parts. Striking 



as the contrast is between the size of the primi- 

 tive arterial trunks and that of the almost in- 

 visible capillary vessels, comparatively few 

 divisions intervene between the two extremes 

 of the arterial system, their number hardly 

 exceeding twenty, as Haller ascertained by 

 counting the divisions of the arteries of the 

 mesentery between the place of their origins 

 from the aorta, and their termination in the 

 capillaries of the intestines.* 



That the arteries in general are circular 

 tubes is evident from an inspection of their 

 orifices when cut across, even in the dead 

 body. The walls of the larger arteries, when 

 empty, collapse, so as to present, on a trans- 

 verse section, an aperture more or less ellipti- 

 cal : when distended, however, either by the 

 blood during life, or by injection in the dead 

 body, these also are circular ; so that the 

 circular form may be considered as universal 

 in all parts of the animal system except at the 

 origins of the aorta and pulmonary artery, 

 where the circumference of each of these ves- 

 sels is distended into three sacculated pouches 

 of equal size, called the lesser sinuses ; and in 

 the ascending portion of the arch of the aorta, 

 which has a dilatation on its right side, in- 

 creasing with years, called the greater sinus. 



The arteries in general become smaller in 

 their course in proportion to the number of 

 branches arising from them. To this, however, 

 there are exceptions, of which the aorta pre- 

 sents a remarkable example, being of as great 

 a capacity near the origins of the primitive iliac 

 arteries as it is in its thoracic portion, and the 

 vertebral arteries are as large where they enter 

 the foramen magnum of the occipital bone as 

 where they arise from the trunks of the sub- 

 clavians, notwithstanding that they have given 

 off many branches in the intermediate part of 

 their course. 



Wherever an artery runs for some distance 

 without giving off branches, it appears to suffer 

 no perceptible diminution in its size, as has 

 been ascertained by the experiments referred to 

 by Baron Haller,! and repeated by Mr. Hunter,}: 

 in which the common carotids were found as 

 capacious near the place of their division into 

 the external and internal carotids as at their 

 origins ; and the same remark being considered 

 as equally applicable to all other arteries simi- 

 larly circumstanced, it has been stated in 

 general terms that the arteries and their branches 

 are cylindrical, and that the whole of the 

 arterial system is a series of cylindrical tubes. 



Although the cylindrical form is pretty 

 general throughout the arterial system, it is by 

 no means accurately preserved. Several arteries 

 increase in size in the progress of their course ; 

 of this we have examples in the umbilical 

 arteries, which expand as they approach the 

 placenta, and the spermatic arteries, especially 

 in the bull and wild boar, which enlarge con- 

 siderably as they proceed to their destination. 

 Moreover, Haller and Martinus have shown 



* Haller, Elementa Physiologiae, t. i. sect. 1. $ 17. 

 t Elementa Physiologiae, t. i. s. 1, 3. 

 $ Treatise on the Blood, &c., p. 168 et seq. 

 4to edit. Lond. 1794. 



Elementa, t, i. s. 3, $ 3. 



