354 Tumors. 



drawn. For this reason visually only the more massive, large and 

 clearly defined bony growths are called osteomata, and the rest 

 are known collectively as ostcopJiytcs. The small protuberances, 

 of the size of a pea to that of a nut, projecting from the surface 

 of bones, are also called c.rosfoscs ; the flat superficial thickenings 

 around bone shafts, periostoscs; those which grow along bones 

 as bony formations in fasciae and connective tissue, parosloses; 

 an ivory-like, hard, well-defined formation in the interior of 

 bones, an cnostosis. Dififuse thickenings of the bones in the 

 skeleton from osseous hyperplasia are known as hyperostoses; 

 osteophytes with cartilaginous coverings, as cartilaginous osteo- 

 phytes. 



The osteophytes and osteomata growing from the skeleton 

 develop principally from the osteoblastic layer of the periosteum 

 or from cartilaginous developmental bases (aulage) ; some are 

 congenital or from their position may be looked upon as caused 

 b\' disturbances of embryonal development and as referable to in- 

 clusive misplacement of bits of the embryonic bone tissue af- 

 fected. This view is especially applicable to the rather common 

 large osteomata of the head cavities (cattle, horses), arising from 

 the sphenoid, ethmoid or the turbinate bones ; in their gradual 

 enlargement they press upon the surrounding bony walls, force 

 the jaw and nose out of position, project into the maxillary sinus, 

 nasal cavities or into the orbit or cranial cavity, and obstruct 

 these spaces with continuous pressure upon the respective soft 

 parts. Other forms which are located on the outside of bones, 

 sometimes as broad expanded growths or arising from slender 

 pedicles, probably are caused by traumatic influences ; and the 

 exostoses which are met commonly in the under jaw of the horse 

 apparently arise from isolated osteoplastic foci ; and the large 

 osteomata on the horn process in cattle are probably due to loss 

 of tissue tension caused by injur}- to the horn capsule. 



A remarkable variety of pathological bone proliferation is the 

 progressive osteitosis met ^^•ith in young dogs. It consists in 

 the occurrence of bone formation at the places of attachment 

 of the tendons and muscles of the lower jaw and extremities, 

 causing as it progressively advances an atrophy of the muscles 

 and giving the animal a stifif awkward gait : it is accompanied 

 by marked thickening of all the bones of the skeleton. The 

 disease is similar to the aft'ection in man known as myositis 

 ossificans progressiva, and is apparently an abnormality of de- 

 velopment, in which as Ribbert supposes the intermuscular con- 



