614 THE BLOOD-VASCULAR SYSTEM OF THE OX 



cover of the flexor carpi internus without giving off any large branches in the fore- 

 arm. It passes through the carpal canal and continues along the inner side of the 

 deep flexor tendon as the volar common digital artery. At the distal third of the 

 metacarpus this vessel is joined by a branch from the internal deep volar meta- 

 carpal artery, forming the superficial volar arch. Near this another branch of the 

 common digital (or of the internal digital) passes around the outer border of the 

 flexor tendons to the posterior face of the metacarpal bone and concurs with the 

 deep volar metacarpal arteries in the formation of the deep volar arch. A branch 

 from the arch passes forward through the inferior foramen of the metacarpal bone 

 and joins the dorsal metacarjial artery which descends from the rete carpi 

 dorsale in the anterior metacarpal groove. 



The volar common digital artery (A. metacarpea volaris superficialis III.) 

 passes into the interdigital sjjace and divides into two volar proper digital arteries, 

 which descend along the interdigital surfaces of the chief digits and pass through 

 the foramina at the upper part of the interdigital surfaces of the third phalanges, 

 enter the cavities in these bones, and ramify in a manner similar to the correspond- 

 ing vessels in the horse. The volar* common digital detaches a branch (A. inter- 

 digitalis perforans) which passes forward through the upper part of the interdigital 

 space and anastomoses with the dorsal metacarpal artery. 



The volar proper digital arteries (or the common digital) give off, in addition to other 

 collaterals, branches which correspond to the arteries of the plantar cushion of the horse. These 

 pass to the bulbs of the claws and anastomose with each other and with the inner and outer 

 digital arteries, forming an arch from which numerous branches are distributed to the matrix 

 of the hoofs. 



The dorsal metacarpal artery (A. met. dorsalis III.) is a small vessel which 

 arises from the rete carpi dorsale, descends in the groove on the anterior face of the 

 metacarpal bone, and is joined by the inferior perforating metacarpal artery from 

 the deep volar arch to constitute the dorsal common digital artery. This vessel 

 (A. digitalis communis dorsalis III.) divides into two dorsal proper digital arteries. 



The internal digital artery (A. digiti III. medialis) is the continuation of the 

 internal deep volar metacarpal artery. It descends on the inner side of the inner 

 digit and terminates at the bulb of the claw by anastomosing with the corresponding 

 volar proper digital artery. It gives off a branch to the rudimentary digit and 

 forms a transverse anastomosis Ijehind the first phalanx with the volar common 

 digital or its inner division. 



The external digital artery (A. digiti IV. lateralis) arises from the deep volar 

 arch, passes down on the outer side of the external digit and is distributed like the 

 inner one. 



BRANCHES OF THE THORACIC AORTA 

 The bronchial and oesophageal arteries often arise separately. 

 Ten pairs of intercostal arteries usually arise from the aorta. The other three 



come from the subcostal artery. 



The two phrenic arteries are very variable in origin. They may come from 



the aorta, the coeliac, left ruminal, or an intercostal or lumbar arter3\ 



BRANCHES OF THE ABDOMINAL AORTA 

 The coeliac artery is al)out four to five inches (ca. 10 to 12 cm.) in length. It 



passes downward and curves forward loetween the rumen and pancreas on the left 



and the right crus of the diaphragm and the posterior vena cava on the right. It 



gives off five chief branches. 



1. The hepatic artery arises from the convex side of the curve of the. coeliac 



artery as it crosses the posterior vena cava. It passes downward, forward, and to 



