CHAP. VII.] THE CATl:i ORGANS OF CIRCULATION. 215 



double set, one deep and one subcutaneous. They moreover com- 

 municate and anastomose together more frequently than do the 

 arteries. The systemic veins are naturally divisible into (1) those 

 which ultimately pour themselves into the vena cava superior, and 

 (2), those which convey blood to the vena cava inferior. To the 

 first category belong the veins of the head, the pectoral limbs, the 

 vertebral column, and part of the thoracic and abdominal walls. To 

 the second category the veins of the pelvic limbs, of the lower part 

 of the trunk, and of the abdominal viscera. 



The veins of the outside of the cranium and face converge to form 

 tlie temporal, internal maxillary and facial reins ; the temporal passes 

 through the parotid gland and becomes (having united with the two 

 others), the external .jugular vein (see Fig. 88), which, be- 

 ginning at the mandibular angle, descends, crossing the sterno- 

 mastoid muscle, to the great subclacian vein. 



The blood from the brain and inside of the cranium collects in 

 reservoirs called the cranial sinuses, which groove the inner surfaces 

 of the bones of the skull.* The blood from all these sources 

 collects at the opening called the foramen lacerum posterius or 

 jugular foramen, and the vein which passes out through it, receives 

 the name of the internal jugular a^ein, which vein descends 

 outside and parallel with the common carotid arter}^, till it joins the 

 subclavian vein (the junction being furnished with a valve), when 

 the two, by their union, form the right innominate (or brachio- 

 cephalic) vein. 



The veins of the digits, fore-paw, and arm of each side, partly 

 unite to form a sub-cutaneous network, which ends in larger channels 

 {radial, ulnar, and median), which unite and end, sooner or later, 

 in the axillary rein. 



The veins of the digits, fore-paw, and arm, also unite to form a 

 deep set of veins which accompany, as rence comites, the tributaries 

 of the brachial rein, uniting and ending ultimately in a single trunk, 

 the AXILLARY VEIN, which, as it passes over the first rib, assumes 

 the title of subclavian, and receives the contribution of the external 

 jugular vein, as already mentioned, as also that of the rertebral 

 vein, which descends through the canal of the cervical transverse 

 processes in company with the ascending vertebral artery. Near 

 the clavicle, the subclavian vein unites with the internal jugular to 

 form the innominate vein already mentioned. Finally, the in- 

 nominate vein unites with its fellow of the opposite side to form the 

 VENA CAVA SUPERIOR, which passcs down in front of the pulmonary 

 vessels of the right side, and to the right of the aorta, to the right 

 auricle. 



Valves are found in the veins of the pectoral limb generally, but 

 especially in the deep veins. 



The veins of the digits, hind-paw, and leg of each side, also partly 



* Tlie middle of the skull roof and tlie occipital and temporal bones as already 

 described, see ante, ])p. 62 and 66. 



