682 THE VEINS. 



ophthalmic artery, that vessel coming from the internal carotid ; but it furnishes all the other 

 branches we have studied in animals. There are, therefore: a tympanic artery; a meningeal, 

 middle, or spheno-spinous ; an anterior and posterior deep temporal ; an inferior dental ; a 

 buccal; a masseteric; pterygoideans ; and a descending palatine or palato-labial artery. 



THIRD SECTION. 

 THE VEINS. 



CHAPTER I. 



GENERAL CONSIDERATIONS. 



Definition. — The veins are the centripetal vessels of the circulatory system. 

 They bring back to the heart the blood which has been carried from that viscus 

 to the organs. 



Division. — Some proceed from the lungs, carrying red blood, and converge 

 towards the left auricle of the heart : these are the pulmonary veins, or veins of 

 the lesser circulation. Others emerge from the mass of all the organs, transport 

 the dark blood, and open into the right auricle : these are the veins of the 

 general circulation. 



There are, therefore, two venous systems commencing by a capillary network, 

 opposite an arterial network. Sometimes a third system of veins has been 

 described for the intestines ; indeed, the vena portse offers a certain indepen- 

 dence in the midst of the veins of the general circulation, as it terminates in a 

 capillary plexus in the interior of the liver, and by this plexus it communicates 

 with the posterior vena cava. 



General Disposition. — The veins, after succeeding the capillary networks 

 which terminate the arteries, or the spaces in the erectile tissues, form a series of 

 convergent ramifications which repeat, in a general manner — but in an inverse 

 gense— the arterial ramifications, the course of which they for the most part follow. 

 A certain number, nevertheless, are placed at some distance from the arterial 

 trunks, beneath the external tegumentary membrane, where they are disposed in 

 a vast network that constitutes the superficictl veins of the body. Apart from 

 this peculiarity, we have nothing more to say with regard to the situation, 

 direction, relations, and anastomoses of the veins than has been already made 

 known in studying the arteries. It is only to be remarked, that the anastomoses 

 of the venous system are more numerous, larger, and more complex than those 

 of the arterial system ; that they also communicate with more voluminous 

 trunks ; and that they very often join the deep to the superficial veins. At 

 certain points— external genital organs, bladder, rectum— the anastomoses are so 

 numerous as to constitute veritable venous plexuses. These are more especially 

 met with in regions where the circulation is liable to be more or less hindered, 

 either from the displacement of organs or variations in their volume. Fenwick 

 has made known some important communications with regard to the mainte- 

 nance of the circulation ; for instance, those between the subcutaneous veins, 

 the laro-e veins of the limbs, and the substance of the thoraco-abdominal 



