CONFORMATION. 439 



Tho eminences and ihe depressions of the inferior head of the upper 

 pastern bone should be well developed, so as to dip well into the corre- 

 sponding parts of the lower or coronet bone. This formation gives 

 strength to the articulation, and eases the strain on the ligaments and 

 tendons. 



904. The Sesamoid Bones. 



The Sesamoid bones (marked 9 in skeleton) are situated at the upper 

 back part of the fetlock. Into them is inserted the superior sesamoideal, 

 commonly called the Suspensory ligament. It is important that these 

 two bone.s should be large and well developed in order to give proper 

 attachment to that important ligament. They also act as rollers for the 

 great flexor tendons of the leg, which pass over them. 



The sesamoid bones are occasionally subject to ulceration, but the 

 disease does not usually originate in them. The tendons, when over- 

 taxed, often become inflamed, and then the bones, over which they pass, 

 become secondarily involved in the neighbouring inflammatory action. 

 (See Plates 25 and 26 on Splint and Plate 27 on Sprains of the Tendons 

 and Ligaments of the Fore-leg.) 



905. The Coffin bone or Os pedis. 



The Coffin bone or os pedis or bone of the foot (k. Fig. 10, Plate 35) 

 varies somewhat in size in different horses. But the size, of the foot does 

 not depend so much on the size of the bone, as on the quality and condi- 

 tion of the crust or horn which encloses the bone. The crust, as the 

 reader is aware, frequently alters in size according to many varying 

 circumstances ; but the bone, we need scarcely say, does not alter in size 

 except in cases of very serious disease. The coffin botie rests on innu- 

 merable springs. Concussion is thereby so expended, as to be greatly 

 lessened in the frame above. 



In the disease, known as Founder, the attachment of the laminae (b b. 

 c c. Fig. 10) to this bone becomes loosened, and the toe of the bone then 

 comes on the sole ; and the peculiar condition recognised as " pumice " 

 foot is produced. See Plate 56, Figs. 23 and 24, for Laminitis, also par. 

 1027. 



906. The Navicular Bone. 



The Navicular is a small bone placed at the inferior and posterior part 

 of the coffin bone (/ Fig. 10). It acts chiefly as a roller for the flexor 

 perforans tendon (m.m. Fig. 10), where it makes its bend prior to inser- 

 tion into the lower part of the coffin bone. 



It is somewhat frequently the seat of disease, especially of caries. The 

 disease appears to originate in the bone from the effect of concussion or 

 other such causes. (See Chapter 65, par. 1021, Navicular Disease.) The 

 tendon, which passes under and round this bone, is very apt to become 

 secondarily involved in the disease affecting the bone ; or it may become 

 sprained at the point marked X in Fig. 10, section of a foot, where it 

 makes its bend round the navicular bone, prior to its insertion into the 

 coffin bone. 



