1890 - 91 .] Drs Symington & Thomson on Defective Ossification. 285 
without its simultaneous removal or absorption in the interior, 
which we described as the prominent feature in the -dong bones. 
Nor can we ascribe the arrest to deficient vascularisation of the 
general cartilaginous mass in which the arrested nucleus is embedded, 
for the number and size of the vascular canals in the cartilage is 
quite equal to the normal. We are absolutely unable to account for 
the arrested growth in the osseous nuclei in the vertebral bodies, in 
the os calcis and astragalus, &c., and also for the complete absence 
of ossifying centres in these bones in which these are normally 
present at birth (e.g., sternum). 
Eberth and Muller are of opinion that the arrested development 
of endochondral bone is the result of an interference arising from an 
enormous overgrowth of the periosteal bone, while Klebs holds the 
view that the origin lies in an imperfect development of the 
medullary vessels supplied to cartilage. We cannot accept the former, 
because it will not hold for the arrest observed in parts of the 
skeleton, e.g., os calcis, where there is no periosteal growth whatever, 
far less excessive growth ; while as regards the latter, our examina- 
tion of the bones does not show any imperfection in the vessels 
supplied to cartilage in hones devoid of an external periosteal crust 
(os calcis). The arteries and nerves of the extremities presented no 
alteration in their microscopical structure. 
Most of the published descriptions of similar specimens indicate 
that the authors are of opinion that it is a real disease of the foetus, 
instead of regarding the condition, as we do, as a simple arrest of a 
normal process. Hence many observers describe it as a foetal form 
of sporadic cretinism, others as a form of foetal rickets. From the 
latter it is readily differentiated. 
Its resemblances to rickets are only apparent, thus : — 
1. The open fontanelles do not indicate hydrocephalus as 
has been assumed, but are simply due to the enlarge- 
ment of the vertex compensatory to the contraction of 
the base. 
2. The contracted chest, the external furrow at the costi- 
chondral junctions, the apparent rosary, are not due to 
rachitic changes, but to the shortness of the ribs from 
arrest of ossification ; the short ribs joining the long carti- 
lages at an angle. 
