596 THE VEINS. 



the predominance of the cranium over the face. This vessel describes a flexuous course 

 until it reaches the carotid foramen in the petrous bone ; it forms two curves in the 

 cavernous sinus, penetrates the dura mater, and divides at the fissure of Sylvius into 

 four branches, which are, as in Solipeds : the posterior communicating, anterior cerebral, 

 middle cerebral, and artery of the choroid plexus. The internal carotid has an 

 important collateral branch, the ophthalmic artery, that arises from the convexity of 

 the curve the carotid makes inside the anterior clinoid process, at the bottom of the 

 orbit. If it differs at 'its origin, yet this vessel has a distribution analogous to that 

 already described. 



EXTERNAL CAROTID ARTERY. In its origin, course, and termination, the external 

 comports itself as in animals. It gives rise to six branches : 



1. The superior thyroid, resembling in its distribution the thyro-laryngeal of 

 Solipeds. 



2. The lingual artery, which furnishes a eublingual, and takes the name of ranine 

 at its termination. 



3. The facial artery, which gives off the palatina ascendens analogous to our 

 pharyngeal, and the submental. 



4 The posterior auricular artery. 



5. The inferior pharyngeal artery. 



6. The occipital. This vessel represents the occipital of the Horse minus its cerebro- 

 spinal liranch. It gives off a mastoid artery, and terminates in the muscles of the neck 

 and on the posterior aspect of the cranium. The cerebro-spinal branch is replaced by 

 the termination of the vertebral artery, which forms on the inferior face of the medulla 

 oblongata the basilar trunk, whose disposition is identical with that already described. 



The superficial temporal artery, and the internal maxillary artery, constitute the 

 termination of the external carotid. 



The internal maxillary is directed towards the spheno-palatine or nasal foramen, 

 into which it passes and terminates as the spheno-spinous artery. It does not give off 

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

 all ihe 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 masscteric ; pterygoideans ; and a descending palatine 

 or paiato-labiul artery. 



THIKD SECTION. 

 THE VEINS. 



CHAPTER I. 



GENERAL CONSIDERATIONS. 



DEFINITION. 'The veins are tlie centripetal vessels of the circulatory 

 system. They bring back to the heart the blood which had been carried 

 from that viscus to the organs. 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 capill 

 network, opposite an arterial network. Sometimes a third system of veil 

 has been described for the intestines ; indeed, the vena portse offers a certaii 

 independence 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. 



EXTERNAL CONFORMATION. The veins, after succeeding the capillary net- 

 work which terminates the arteries, or the cells of the erectile tissues, 



