186 CIRCULATORY SYSTEM. 



enters a groove scooped in that bone, and is conducted obliquely 

 forward and inward, into the foramen in the posterior concavity 

 of the bone. Here we lose sight of it altogether — the knife and 

 forceps no longer avail us to discover its progress and destination : 

 either the bone must be chiselled away, or (the vessels being pre- 

 viously injected) be eroded by maceration in an acid. We shall 

 then detect the artery in the interior of the coffin-bone, making a 

 turn outward again, and subsequently another inward, in the 

 course of which, meeting with its fellow, the two trunks coalesce, 

 and in so doing form an arterial semicircle corresponding to the 

 circumferent line of the edge of the os pedis, which has been 

 very properly named by the Professor, the circulus arteriosus*. 

 The plantar vessels and nerves are invested in the course of their 

 descent to the foot by cellular substance, which binds them loosely 

 to the parts contiguous, whereto they pass. This accounts for 

 their canals being flexuous when distended with injection, or when 

 the foot is flexed upon the fetlock ; a circumstance that seems to 

 have escaped the notice of writers on the foot. The branches of 

 the plantar artery are many and important. After detaching some 

 small ramifications inwardly to the fetlock, posteriorly to the flexor 

 tendons, which anastomose with their fellows, and anteriorly to 

 the extensor tendon, which are also anastomotic, it sends off' — 



1. The perpendicular artery, a little above the mid- 

 dle of the OS suflfraginis : a slender branch that descends upon 

 the side of the bone, inclining forward, and ends in the space 

 above the coronary ligament in anastomosis with its fellow, form- 

 ing an arch, presenting its convexity downward, called the super- 



Jicial coronary , from which emanate about eighteen small descend- 

 ing arteries that run down over the coronary plexus of veins, 

 whose principal function, it is said, is *' to secrete the crust." I 

 would beg to remark here, however, that, although I believe what 

 ] give to be the ordinary arrangement of these arteries, there is 

 so much variation to be found in different subjects, that I cannot 

 vouch for the unexceptionable correctness of this description, how- 

 ever I may stand amenable for its general accuracy. The plantar 

 trunk having detached various small unimportant branches back- 

 ward, the great design of which appears to have been to preserve 

 free and uninterrupted intercourse with the opposite trunk, it 

 next sends off", below the pastern-joint, 



2. The transverse artery, which proceeds directly across 

 the front of the os coronse, underneath the extensor tendon, to 

 join its fellow branch from the other side, the two together form- 

 ing the superior coronary/ circle: this pours most of its blood 

 through two short lateral conduits, the communicating arteries, 



* Professor Coleman, " On the Foot of the Horse" vol. ii. 



