REGIONAL ANATOMY 17 
end on 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 burse, 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. 
Tue Extensor Pepis.—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. 
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