DISSECTION OF THE DOG 129 



V. mediana cubiti. — The median vein begins by draining the first 

 digit. After crossing the medial aspect of the forearm it comes to occupy 

 the groove between the extensor and flexor mass of muscles. The termina- 

 tion of the vein on the flexor aspect of the elbow-joint has already been 

 examined. 



V. eadialis. — The large radial vein commences as the dorsal veins of the 

 second to the fifth digits. Just above the carpus a considerable augmentation 

 of volume results from the reception of a large branch from the median vein. 

 The radial vein now follows the anterior border of the forearm, and ends 

 by assisting the median cephalic vein in the formation of the cephalic 

 vein. 



Vv. Ulnae.es. — One or two small ulnar veins will be found over the 

 posterior and medial part of the proximal third or so of the forearm. They 

 may join the basilic vein. 



A. eadialis collateealis PEOXiMALis. — The proximal radial collateral 

 artery, a branch of the brachial, enters the forearm by crossing the surface 

 of the biceps muscle. A division into two branches takes place. The more 

 lateral and larger of the two passes into the metacarpus and terminates as 

 three common dorsal digital arteries (aa. digitales dorsales communes II, III, 

 et IV) which lie in the grooves between the second and third, third and fourth, 

 and fourth and fifth metacarpal bones. 



N. ctjtaneus antibeachii LATEEALis. — The lateral cutaneous nerve, a 

 branch of the musculo-cutaneous, enters the foramen between the biceps and 

 brachialis muscles, and then follows the median vein. 



N. eadialis. — The superficial branch of the radial nerve travels down 

 the forearm in company with the radial vein. About the level of the elbow 

 it divides into medial and lateral' branches. The medial branch, the smaller 

 of the two, accompanies the communicating vein from the median to the radial 

 vein and ends as the dorsal nerves of the first and second digits. 



The lateral branch crosses the extensor aspect of the carpus and terminates 

 as dorsal nerves of the second, third, fourth, and fifth digits. 



Deep fascia. — The deep fascia of the forearm is strong and thick. It 

 forms a sheath for all the muscles and passes between them as intermuscular 

 septa. At the borders of the limb it is attached to the radius and ulna, and at 

 the distal end of the radius forms an annular ligament by which the tendons 

 of the extensor muscles are retained in place. 



Dissection. — The deep fascia must be removed in order to allow of the 

 examination of the anterior and lateral regions of the forearm and the 

 dorsum of the manus. The annular ligament, however, must be left in 

 position for the present. 



It is convenient to note here that the annular ligament has bony attach- 

 ments at five places. The result is that four passages in which tendons are 



