THE COFFIN JOINT 419 



THE COFFIN JOINT 



The coffin joint is made up of the lower end of the os coronrp, inserted 

 in the concavity of the pedal bone, and supported behind by the navicular 

 bone. These are lined by one continuous synovial capsule, and protected by 

 ligaments which may be divided into two sets. First, those connecting the 

 OS coronfc to the os pedis. Secondly, that between the os naviculare and the 

 OS pedis, which is of an interosseous charactei', being short, and composed of 

 veiy strong fibres ; and tJdrdly, the ligament on each side connecting the os 

 naviculare with the coronet. 



1. The coroiio-pedal ligaments are two on each side, one anterior and the 

 other posterior. The former consist of two large, thick and short bundles of 



Fig. 53.— rosTr.RiOR View of 

 THE Coffin Joixt. 



A. Coronal bone. 



13. Navicular bone. 



G. Pedal bones. 



1. Corono-navicular ligament. 



•-'. 2. Lateral ligaments of the 



navicular bone. 

 3. Pcdo-uavicular ligament. 



ilbres attached above to the sides of the os coronoe, and below to the lateraf 

 edges of the cacumen coronte of the pedal bone (see page 418). Each is 

 partly covered posteriorly by the lateral cartilage in which it becomes lost, 

 while the anterior edge is continuous with the tendon of the extensor pedis. 

 The ijosterior lateral ligament on each side commences above from the lower 

 fibres of the lateral ligament of the pastern joint, and from the sides of the 

 lower end of the os coronte. It descends obliquely backwards, and is inserted 

 in the retrossal process of the pedal bone, and in the upper edge of the 

 lateral cartilage. 



2. Between the os navicidare and the os pedis is a very short but strong 

 band of fibres in the nature of an interosseus ligament. It arises from the 

 groove on the lower and fore edge of the os naviculare, and passes forward 

 to be attached to the back part of the plantar surface of the pedal bone, 



3. Tivo lateral ligaments, one on each side, attach the os naviculare to the 

 sides of the coronal bone. 



The synovial membrane is inserted around the margins of the cartila- 

 ginous articular sui-faces of the os coronte, os pedis, and os naviculare ; in 

 front it is attached to the tendon of the extensor pedis, at the posterior part 

 of the os naviculare, and between this sui'face and the tendon of the flexor 

 pedis perforans another capsule occurs. 



The movements of the coffin joint are similar to those of the fetlock and 

 pastern, with the addition of a very limited gliding motion enjoyed between 

 the OS naviculare and os pedis. 



