560 DISEASES OF THE ORGANS OF LOCOMOTION. 



by inspiratoiy dilatation of the thorax. Any point of the ribs where 

 an elastic ligament replaces the bone would become depressed on in- 

 spiration. Curvatures of the upper and lower ends of the individual 

 vertebrae cause distortion of the spinal column ; curvatures of the pel 

 vie bones at their points of union cause pelvic deformities ; the most 

 frequent form is the so-called rachitic pelvis, where the antero-posterior 

 diameter is shortened, but occasionally, also, when the curvature does 

 not occur at the point of union of the sacrum with the ilion, but at 

 that of the pubis with the ischium, we have a heart-shaped deformity. 

 In the angular deformities the bone is only curved on the convex side, 

 but on the concave side it is actually broken. The medullary cavity 

 of a sharply-bent bone is, like the cavity of a sharply-bent quill, 

 greatly contracted at the bent portion, and is subsequently entirely 

 closed by callus. Total fractures, also, are not rare in rachitic bones, 

 but they differ from fractures of healthy bones, in never being accom- 

 panied by injury of the periosteum, which is separated from the com- 

 pact bone-substance by a soft, incompletely-ossified layer. The sutures 

 of the skull, which correspond to the epiphyses of the long bones, ossify 

 very late ; hence, in rachitic children even two or three years old, we 

 not unfrequently find the fontanelles still open, and so large as to in- 

 duce the suspicion of chronic hydrocephalus. The bones of the head 

 and face, which correspond to the diaphyses of the long bones, undergo 

 the same changes as the latter do ; imperfect ossific proliferations of 

 the periosteum occur on the bones, especially near their edges, and de- 

 form the head and face. Besides this thickening, a partial thinning of 

 the cranial bones is also observed in rachitis (Elsasser*s soft occiput, 

 craniotabes). This thinning, which may finally let the dura mater 

 and pericranium come in contact, results from gradual disappearance 

 of the cranium under the pressure of the gradually-increasing brain, 

 which is not accompanied by coincident formation of new bone-sub- 

 stance on the surface of the skull. These membranous spaces are 

 most frequently observed in the occiput, more rarely in the parietal or 

 frontal bones; they occur chiefly at places where the impressiones 

 digitatae, corresponding to the convolutions of the brain, are normally 

 found. A symptom analogous to craniotabes is also seen in the 

 lower jaw, the anterior wall of the alveolus being often perforated by 

 the milk-teeth. If the rachitis goes on to recovery, the swelling of the 

 articular ends of the bones subsides ; the bones become firm, while 

 only a small amount of the curvature of the limbs is corrected ; after 

 the disease has run its course, the cartilaginous proliferations of the 

 epiphyses often ossify sooner and more completely than is desirable 

 for the longitudinal growth of the bones, for which it is necessary that 

 the epiphyses should remain cartilaginous. It is, probably on this ao 



