12 Williams, Fisher, and Udall: The Spavin Group. 
the humerus contained an ulcerlike depression, one-half by five-eighths 
of an inch in size; a similar roughness was present on the articular 
surface of the ulna. Carpus: cartilage slightly eroded between the 
articular surfaces of the os magnum and radius, and between the small 
carpal and metacarpal bones; on microscopic examination the cartilage 
was found torn, villous, and fibrous; the cartilage cells proliferated and 
enclosed in mother capsules. The osseous tissue of the os magnum was 
abnormally hard and many of the marrow cavities were empty, while others 
were completely filled with marrow cells; the canaliculi of the lacunz had 
undergone marked atrophy, this was also true of the protoplasmic ex- 
tensions of the bone corpuscles; many of the bone corpuscles (cells) 
within the lacune assumed a roundish form. : 
Right posterior extremity: femoro-patellar articulation: the synovial 
fluid had increased in amount; the articular cartilage presented extensive 
erosion on the inferior surface of the patella; the entire surface of the 
fibro-cartilaginous process eroded; the corresponding surface of the 
femur had undergone similar changes but not discolored. Femoro-tibial 
articulation: cartilage extensively eroded, in places the atrophy was com- 
plete. One of these areas presented a polished surface one and one-fourth 
inches by three-fourths of an inch in diameter, portions of the cartilage in 
places had undergone osseous degeneration. The histological changes 
identical with those of the carpus; metaplasia of the cartilage matrix and 
arrangement of the proliferated cartilage cells in mother capsules. Tarsus: 
cartilage absent over a small triangular area on the distal extremity of the 
tibia; bony exostosis in the form of a spavin. Fetlock: discoloration and 
roughness on the internal condyle of the first phalanx. 
Left posterior extremity: femoro-tibial articulation: cartilage rough- 
ened; synovial membrane discolored; capsular ligament thickened; the 
histological changes were the same as previously described. Tarsus: tibio- 
astragaloid articulation: normal. Astragalo-scaphoid articulation: car- 
tilage atrophied in the form of erosion-like ulcers that reach to the bone; 
bursa of cunean tendon normal. Fetlock: cartilage and bone normal: 
tendon sheaths discolored. 
Conclusions; An examination of the bones of this animal suggested 
that the diseased processes were well advanced. Exostoses and pro- 
liferative changes in general seem to have reached a termination; the 
solidity of the bone itself and appearance in the marrow cavities indicated 
a condensing stage of the disease. Although a few of the marrow cavities, 
were entirely filled with cells the greater number were comparatively 
empty so that large open spaces were visible. (Figs. X and XI.) 
Case II.—A small bay mare, advanced in age, brought to the clinic 
to be destroyed because of chronic navicular disease. Clinical examination 
revealed no exostoses. 
Autopsy:— Right anterior limb: bursa podotrochlearis: cartilage and 
tendon roughened, the bone was also affected. Suffragino-coronal articu- 
Jation: the proximal extremity of the second phalanx presented areas of 
discoloration near the center, upon removal of the apparently normal car- 
tilage these punctiform areas were seen to be present in the bone. 
Left anterior limb: articulations apparently normal. Bursa podotro- 
