642 CIRCULATORY SYSTEM OF THE DOG 



The vena azygos resembles that of the horse, and receives at the ninth or 

 tenth thoracic vertel^ra a vena hemiazygos. 



Two jugular veins are present on each side. The external jugular vein is 

 formed by the union of external and internal maxillary veins at the posterior Ijorder 

 of the submaxillary gland. The two external jugulars are commonly united by a 

 transverse branch below the cricoid cartilage. Each passes along the neck on the 

 sterno-cephalicus, covered only l^y the skin and panniculus, dips under the cleido- 

 cervicalis, and joins the internal jugular. 



The external maxillary vein arises on the lateral nasal region by the junction 

 of the dorsal nasal vein with tlie angularis oculi. Near the infraorbital foramen it 

 receives the lateral nasal vein, and a little lower the superior labial. In its course 

 along the anterior border of the masseter it receives the vena reflexa, which arises 

 in the ptery go-palatine fossa by the junction of infraorbital, sphenopalatine, and 

 palatine radicles, together with a branch from the cavernous sinus. At the lower 

 border of the mandible it is joined by the inferior labial vein, which receives the 

 buccinator vein. The lingual vein is connected with its fellow Ijy a superficial 

 transverse branch at the insertion of the sterno-hyoidei. The sublingual and 

 submental veins terminate in a variable manner, but often form a common trunk 

 which joins the lingual. 



The internal maxillary vein arises from the pterygoid plexus, formed chiefly 

 by dorsal lingual, inferior alveolar, deep temporal, pterygoid, and meningeal tribu- 

 taries. It receives the superior cerebral, auricular, superficial temporal, transverse 

 facial, and masseteric veins, and often a trunk formed by the union of the inferior 

 cerebral and occipital veins. 



The internal jugular vein results usually from the junction of laryngeal and 

 thyroid veins, but in some cases it is formed by the confluence of the inferior cerebral 

 and occipital veins. 



The brachial and radial veins are satellites of the arteries. 



The ulnar vein is usually doul:)le. It unites below the carpus with a branch of 

 the interosseous vein to form the superficial venous arch. 



The cephalic vein accompanies the ulnar artery in the forearm and joins the 

 superficial venous arch below. 



The accessory cephalic vein arises from the union of three dorsal metatarsal 

 veins. It joins the cephalic about the middle of the forearm. 



There are three short volar metacarpal veins which open into the superficial 

 venous arch. They are formed above the metacarpo-phalangeal joints l)y the 

 junction of the volar digital veins, of which there are two for each of the chief 

 digits. The volar vein of the first digit joins the superficial venous arch. 



Each of the chief digits has two dorsal digital veins, while the first digit has one. 



The posterior vena cava, its collateral affluents, and common iliac radicles 

 present no si^ecial features of importance. 



The internal iliac vein corresponds in regard to its tril)utaries with the liranches 

 of the artcr\', exce]:)t that it is not divided into dorsal and ventral l)ranches. 



The external iliac, femoral, and popliteal veins with their collateral trilnitarics 

 are satellites of the arteries. 



The anterior tibial vein is usually double, and the posterior tibial vein is very 

 small. 



The internal saphenous vein is the upward continuation of the internal plantar 

 metatarsal vein. It communicates by a large branch with the dorsal metatarsal 

 vein, and ascends the leg as a satelHte of the saphenous artery and its plantar 

 (posterior) branch. The recurrent tarsal or external saphenous vein is larger. 

 It is formed at the lower part of the leg by the union of dorsal and external plantar 

 metatarsal veins, crosses the outer surface of the leg obliquely upward and back- 

 ward, ascends behind the gastrocnemius and joins the posterior femoral vein. 



