284 CHARLES It. STOCK AI! I) AND A. L. JOHNSON 



in plate 52 arc from his report. The deficiency in basicranial 

 Length fails to give enough support in a forward direction 

 to the unions between the wings of the sphenoid and the 

 frontal bones. This apparently insufficient support causes the 

 ethmoid bone and the orbital plates of the frontal bone to 

 sag inward and back, depressing the nasion and causing the 

 bulging rounded shape to the forehead. The mature face of 

 the human achondroplasic is wide, with a depression at the 

 nasion ; the nose bridge is low and the nose short and inclined 

 to be upturned at the nostrils; and the maxilla is short and 

 somewhat set-back, causing prognathism of the mandible 

 which projects beyond the maxilla with the lower incisors 

 biting in front of the upper. All these facial conditions are 

 quite directly related to the shortened and defective basi- 

 cranial bones. 



A photograph of the skull of a young puppy cut through 

 the sagittal plane is shown in figure 3. In the puppy, the 

 basicranium is composed of three parts, instead of two as 

 in the child, and this arrangement may have some connection 

 with the production of a long muzzle and extension of the 

 entire facial skeleton. The posterior basicranial epiphyseal 

 cartilage in the puppy skull lies between the basioccipital 

 and basisphenoid bones, and thus corresponds to the single 

 cartilage in the same location in the human skull. The more 

 anterior basicranial cartilage in the puppy is inserted im- 

 mediately in front of the part of the sphenoid forming the 

 sella turcica, and it therefore intervenes between two parts 

 of the immature sphenoid bone. The base of the dog's skull 

 grows in length by means of these two cartilages. The effects 

 on skull pattern due to this growth are quite similar in both 

 the human and the dog. The newborn puppy of all breeds 

 is round headed and rather flat faced, and the long jaws 

 and muzzle of the adult dog are almost entirely postnatal 

 developments. 



The skulls of two newborn puppies are photographed to- 

 gether from the ventral aspect in plate 53 (figs. 1 and 2). 



