466 THE ANATOMY OF THE HORSE 



to the bones of the tail, along which it ramifies. Lastly, the gluteal 

 artery passes out of the pelvis through the hole in the sacro-sciatic 

 ligament in company with the sciatic nerve, and supplies muscular branches 

 to the glutei. 



The external iliac artery is smaller than the internal, and takes the 

 same course as far as the articulation, beyond which it passes; lying just 

 within the brim of the pelvis, in close contact with the psoas and iliacus 

 muscles and covered by the peritoneum. About midway between the 

 symphisis pubis and the anterior spinous pi-ocess of the ilium it gives off 

 the circumflex artery of the ilium, and then receives the name of the 

 femoral artery. At this point the femoral . vein lies posterior to it, and it 

 is also accompanied by the internal saphena nerve. Proceeding in an 

 oblique direction down the middle of the haunch, it reaches the hollow at 

 the back of the stifle joint, where it is called the 2^opUtcEal artery, and 

 opposite the head of the tibia this bifurcates into the anterior and ^wsterior 

 tibial arteries. Just after emerging from the pelvis it gives off a con- 

 siderable hv&xxch, 2'>rofunda femoris, then the epigastric; and in running 

 down through the muscles of the thigh it gives off numerous small branches 

 to them. 



THE VEINS 



The veins generally correspond with the arteries, the blood of which 

 they return to the heart. Thus there is a large vein which conveys all the 

 blood from the anterior half of the body supplied by the anterior aorta, and 

 this is called vena cava anterior. In a similar manner the jwsterior vena 

 cava is made up of veins which accompany the several arteries that are 

 found throughout the body, with one remarkable exception connected with 

 the secretion of bile. If the splenic and mesenteric veins are traced they 

 will be found to unite together into a lai-ge trunk, which, instead of going 

 on to empty itself into the vena cava posterior, enters the liver, where it is 

 called the vena portce, and branches out again like an artery, the general 

 purposes of which it serves by furnishing blood for the secretion of bile. 

 This will be more fully described under the head of the liver, in the next 

 chapter. From the terminations of the portal veins and hepatic artery the 

 hepatic veins arise, and these empty themselves into the posterior vena 

 cava, just behind the diaphragm. Besides that brought by the two venae 

 cavse, the blood from the heart itself enters the auricle through the coronary 

 veins. 



Although, in general, the veins and arteries correspond in their rami- 

 fications, yet there is a lai-ge class of superficial veins which are not 

 accompanied by any of the latter vessels. In horses which for many 

 generations have been accustomed to fast work, these superficial veins 

 are strongly developed, and are particularly plain in the Arab and his 

 descendants. As a consequence of this, and of the fact that many of the 

 arteries are accompanied by two veins, the whole number of veins is much 

 greater than that of the arteries, and the internal area of the former may 

 be considered to be nearly double that of the latter. In their walls the 

 veins are much thinner tliau the arteries, though like them they have 



