282 CHAELES R. STOCKARD AND A. L. JOHNSON 



Plate 52 (fig. 1) shows the central portion of the basal 

 aspect of a skull from a four year old child. The basioccipital 

 bone is shield-shaped in outline and separated from the 

 lateral occipital portions by thin plates of cartilage, shown 

 as dark transverse lines, near the anterior ends of the con- 

 dyles. The anterior surface of the basioccipital is separated 

 from the basisphenoid by a wide space which was, in life, 

 occupied by the thick growth cartilage. In the human skull 

 this cartilage persists until between the twentieth and twenty- 

 second year and functions to produce the bone growth which 

 brings about an almost continuous lengthening of the basi- 

 cranium with the forward development and strengthening 

 of the upper facial skeleton. At about the age of twenty 

 years this basicranial cartilage becomes ossified, and com- 

 plete ankylosis is established between the basioccipital and 

 basisphenoid bones. The ossification of the cartilage ends 

 the growth in length of the basicranium. 



The formation of the achondroplasic skull, bulldog type 

 head, centers very closely around a defective growth reaction 

 of the basicranial epiphyseal cartilage. This defective growth, 

 however, is anticipated by an earlier deficiency in the carti- 

 laginous matrix which is the precursor of the basioccipital 

 and basisphenoid bones themselves. A section through 

 the sagittal plane of the head of a normal newborn human 

 (fig. 2) shows, in dark color, the well formed and strongly 

 developed hard basioccipital and basisphenoid bones, with, 

 in lighter color, the thick epiphyseal growth cartilage between 

 them. A similar section from the head of a newborn human 

 achondroplasic (fig. 4) shows a very different condition. The 

 basioccipital bone is short and defective in outline, and the 

 bony basisphenoid is irregular in shape and much below 

 normal in size. These two bones are, at the time of birth, 

 already fused together in places, and the growth cartilage 

 is very dystrophic. These facts were well described by F. 

 Knotzke in 1929 in a report on the pathological anatomy of 

 chondrodystrophy in a newborn baby, and figures 2 and 4 



