MUSCLES OF THE ANTERIOR LIMBS. 263 



maintained against that membranous expansion by a wide fibrous sheath, 

 through which it glides by the aid of two synovial membranes. This 

 tendon is crossed above the knee by that of the oblique extensor, which 

 passes to its surface. 



Action. The name of this muscle indicates its function ; it extends the 

 metacarpus on the fore-arm. 



2. OUique Extensor of the Metacarpus. (Figs. 119, 13; 121, 21 ; 122, 14.) 



Synonyms. Cubito-premetacarpeus, or radio-premetacarpeus Girard. It is the 

 representative of the long abductor and short extensor of the thumb in Man. (Extensor 

 metacarpi obliquus vel parvus PercivalL Radio-metacarpeus Leyh.) 



Situation Form Structure Direction. A small muscle situated at the 

 internal side of the radius, beneath the anterior extensor of the phalanges, 

 penniform in shape, strongly aponeurotic, and terminated by a tendon which 

 turns obliquely round the anterior aspect of the radius in passing 

 downwards and inwards, to reach the oblique channel on the inferior 

 extremity of that bone, and to pass from thence to the inside of the knee. 



Attachments. It has its origin on the external side of the radius ; its 

 terminal tendon is fixed into the head of the internal metacarpal bone, by 

 its fibres becoming confounded with those of the internal ligament of the 

 carpus. 



Relations. This muscle is covered by the anterior extensor of the 

 phalanges and the antibrachial aponeurosis. It successively covers the 

 anterior face of the radius, the tendon of the anterior extensor of the 

 metacarpus, the radial groove lodging its tendon, and in which it glides 

 by means of a small synovial bursa, as well as the internal ligament of the 

 carpus. 



Action. It extends the metacarpus, and may make it pivot from within 

 forwards. 



3. Anterior Extensor of the Phalanges. (Figs. 119, 14 ; 121, 15 ; 122, 9.) 



Synonyms. Epicondylo-prephalangeus Girard. The extensor communis digitorum 

 of Man. (Extensor pedis PercivalL Humero-prephalangeus Leyh.) 



Situation Direction Extent Form Structure. This is a long vertical 

 muscle, situated external to, and behind the anterior extensor of the metacarpus, 

 which it resembles in being composed of a fleshy and a tendinous portion. 

 The muscular portion extends from the inferior extremity of the humerus to 

 above the lower third of the radius ; it is fusiform in shape, intersected by 

 aponeurotic lamellae, and bifid at its superior extremity. 1 The tendinous 

 portion forms two unequal cords, which succeed the two terminal branches 

 of the muscular part, and lie close to each other. These two cords enter 

 the most external of the three grooves in front of the inferior extremity of 

 the radius, and reach the anterior face of the carpal capsular ligament, 

 against which they are maintained by an annular ligamentous apparatus. 

 After passing from beneath this ring, the smallest, which is the most external, 

 joins the tendon of the lateral extensor (Fig. 119, 15). The principal branch 

 (Fig. 119, 14') continues its course on the anterior aspect of the middle 

 metacarpal bone and articulation of the fetlock, until it arrives in front of 

 the digit ; here it terminates on the os pedis, after widening in a remarkable 

 manner, and after receiving, laterally, at the middle of the first phalanx, a 



1 This division, which has been noticed by several writers, has not been shown in 

 figure 119. This is a mistake, as it is constantly present. 



