32 ANATOMY IN A NUTSHELL. 



fillers in it and supplied with vasomotor nerve- (vaso-constrictor and vaso- 

 dilator). These nerves run in the same -heath and are part of the sympathet- 

 ic nervous system. The vaso-constrictor acts to a greater or lesser degree at 

 all times; the vaso-dilator acts upon the constrictor and inhibits its action. 



The artery which passes over a joint gives off branches above and below 

 the joint and these branches run towards the joint and join one another. This 

 joining is called anatsomosis. Its purpose is for the blood to run in these small 

 arteries as a mean- of passing the joint when the main one is closed. This cir- 

 culation i- called collateral. Arteries and veins hear a certain relation to one 

 another. 



Rule.— (Plate VIII.) Above the diaphragm veins are are on the same 

 level, or in front of their companion arteries. Below the diaphragm the arter- 

 ies are on the same level, or in front of their companion veins, excepting the 

 renal and the profunda. 



The tYtiis gets it- food and oxygen from the placenta, while after birth the 

 food come- through the alimentary canal and the oxygen through the lungs. 

 In tracing the circulation after birth we start with the blood in the right auricle: 

 a systole of the heart -ends it through the tricuspid valve into the right ven- 

 tricle; here a systole sends it through the semilunar valves into the pulmonary 

 artery ami the lungs, where it gives n{] carbon dioxid and receives oxygen; it 

 i< continued from the lungs through the pulmonary veins (three to five) to the 

 left auricle of the heart, then a systole sends it through the bicuspid valve into 

 the left ventricle; from here a systole sends it through the aorta to all parts of 

 the body, to pas- through the capillaries and to be collected into the superior 

 and inferior vena- cava- which empty into the right auricle of the heart. 



Veins have valves which keep the blood from running back in its course. 

 All veins do not have valves; some of those which do not have valves are the 

 veins of the dura mater, or sinuses, the pulmonary veins, veins of the portal 

 system and those of the spinal cord. The others will be mentioned when 

 described. 



Arteries a- a rule do not have valves, but there is an exception to this also; 

 the pulmonary artery has valves. Veins receive tributaries, or radicles; arter- 

 ies break into branches. The portal vein breaks into branches like an artery 

 and the vertebral arteries join like a vein to make the basilar artery. The 

 veins are in two -el-; the superficial and the deep; the superficial ones are in 



the superficial fascia, but send communicating branches to the deep veins. 

 The deep veins accompany the arteries in the extremities and there are two for 



each artery: they are called vena' comites. They are presenl in the arm and 

 forearm and from the knee to the ankle, but not from the hip to the knee. The 

 veins are larger than the arteries. If they were all put into one vessel it would 

 be the shape of ;1 cone with the apex at the heart ami its base at the surface of 

 tli.' body because the combined area of the tributaries is greater than that of 

 the main veins. 



