REGIONAL ANATOMY 17 



end of the extremities and posterior surface of the navicular 

 bone. Having reached that position, they send short 

 attachments to the retrossal process of the os pedis and to 

 the inner face of the lateral cartilage. 



Synovial Membrane. — This extends below the facets 

 uniting the navicular to the pedal bone, and offers for 

 consideration two sacs. A large one posteriorly running 

 up behind the second phalanx to nearly adjoin the sesa- 

 moidean bursa?, and a small one, a prolongation of the 

 synovial membrane between the antero-lateral and postero- 

 lateral ligaments of the same side. This latter is often 

 distended, and on account of its close proximity to the seat 

 of operation, is liable to be accidentally opened in excision 

 of the lateral cartilage for quittor. 



C. THE TENDONS. 



In order to convey an intelligent understanding of the 

 tendons it will be wise to briefly describe the course of 

 their parent muscles from their commencement. 



The Extensor Pedis. — The extensor pedis arises from 

 the lower extremity of the humerus in two distinct portions 

 of unequal size, a muscular and a tendinous. These are 

 succeeded by two tendons passing in common through a 

 vertical groove at the lower end of the radius. Lower in 

 the limb these tendons separate, the outer and smaller 

 joining the tendon of the extensor suffraginis, and the 

 inner and main tendon continuing its course downwards. 

 With the exception of the navicular, it is attached to all the 

 bones of the foot, and is covered internally by the capsular 

 ligaments of the joints over which it passes, those with 

 which we are concerned being the pastern joint and the 

 pedal joint. Before its attachment to the os pedis it 

 receives on each side of the middle of the first phalanx 

 reinforcement in the shape of a strong band descending 

 obliquely over the fetlock from the suspensory ligament. 

 Widening out in fanlike fashion, it is inserted into the 

 pyramidal process of the os pedis. 



