146 NEW YORK ZOOLOGICAL SOCIETY: 
frequent in the straight-backed monkeys (see plate 2) as in 
those which present a normally curved spinal column. The 
position, already described, which the animal early begins to 
assume is doubtless largely responsible for this very marked de- 
formity. 
The thorax presents some of the most typical malformations. 
The lower ribs generally become more widely separated, while 
the upper ones, particularly those to which the pectorals are 
attached, become bowed in, sometimes forming a peculiar letter 
S deformity (see plate 3). Ordinarily this causes a throwing 
forward of the sternum, producing in some cases a typical “pigeon 
breast” (see plate 3). The points of juncture of the ribs with 
the costal cartilages become enlarged, causing nodes like those 
typically seen in rachitis (the “rachitic rosary’). Special types 
of deformity of the thorax may be seen, depending largely on 
the physical habits of the particular animal and on the character 
of the spinal column deformity. 
The bones of the lower extremity are usually more or less 
deformed, ununited fractures may be present, surrounded by un- 
calcified fibrous callus. As a rule, an outward lateral curvature 
is presented, but on account of the early paralysis and since the 
animal very soon learns to support itself on the upper extremities, 
swinging the body between the arms as in using crutches, the 
relief of weight from the lower extremities doubtless prevents 
extreme deformity of the bones. In our opinion the bony 
changes are inaugurated in the bones of the lower extremities, 
if we may judge from the symptoms first manifested and from 
the earliest development of deformity. The ends of all the long 
bones frequently become enlarged. 
Changes in the pelvis are not very marked and, as a rule, the 
form is fairly well preserved, but, consequent upon deviations 
of the column, various lateral deflections may be seen. The most 
frequent deformity, while not really one of the pelvis itself, is 
the development of an unusually acute angle at the juncture with 
the lumbar and sacral column. 
Deformities in the upper extremities are not usually present, 
except for increase in size of the epyphyseal ends of the bones 
and, as a rule, these appear rather late in the disease. This is 
probably due to the fact that involvement of the upper extremities 
of the animal are among the very later stages of the disease, and 
ordinarily before the animal has proceeded so far he has either 
succumbed to the terminal processes or, having become unfit for 
exhibition, has been killed. 
