54 



TOPOGKAPHICAL ANATOMY OF 



position of the metacarpal bones and the first phalanx. A large amount 

 of the anterior (dorsal) surface of the third metacarpal bone can be felt 

 through the skin. The tendons of the digital extensors, however, over- 

 lie it in part, and their position should be determined by palpation. 

 The small second and fourth metacarpal bones should be followed 

 from the vicinity of the carpus to the distal third of the meta- 



!M. extensor carpi radialis. 



M. extensor digitorum commimis. 



V. cephalica antibracliii. 



A. metacarpea volaris 

 medialis. 

 A. digitalis communis. 



N. volaris medialis. ' 



M. llexor digitorum subliniis. 



M. extensor digiti 

 quinti. ^^^ 



Accessory carpal 

 bone (pisiform). 



M. extensor carpi 

 ulnaris. 



UL. 



^ M. llexor digitorum 

 profundus. 



N. ulnaris (ramus 

 superflcialis). 



N. volaris 

 lateralis. 



N". ulnaris (ramus profundus). 

 A. metacarpea volaris lateralis. 



Fig. 36.— Section across the Most Di.stal Part of the Forearm at the Level indicated by F 



ill Fi«. 30. 



carpal region, where commonly their expanded distal ends can be 

 detected. 



The prominent line of the flexor tendons can be followed with ease. 

 Between them and the metacarpal bones is a groove on each side of the 

 limb, and herein a gradually increasing ridge — formed by the middle 

 interosseous muscle — can be determined. 



Over the prominence corresponding to the sesamoid bones of the 



first phalanx is a tuft of long hairs (their length varies with the breed 



of horse) among which a horny callosity, the "ergot," will be found 



resting upon a fibrous cushion. It is generally accepted that the 



"ergot" is the ^lomologue of the large central foot-pad of the dog; 



and it is assumed that, though now rudimentary and vestigial, it 



was of considerable functional importance in those ancestors of the 



horse that were digitiaradfi. , . ... „^ 



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