Volume L August, 1897. Number I. 



ZOOLOGICAL BULLETIN. 



THE MORPHOLOGY OF THE PETROSAL BONE 



AND OF THE SPHENOIDAL REGION OF 



THE SKULL OF AMIA CALVA. 



EDWARD PHELPS ALLIS, JR. 



THE sphenoidal region of the skull of vertebrates is that 

 part of the base and sides of the skull that corresponds to 

 that part of the skull of man that is occupied by the sphenoid 

 bone. This bone in man (No. 24, vol. ii, pt. i) lies be- 

 tween the ethmoid bone anteriorly and the occipital and 

 temporal bones posteriorly, and has two portions, an anterior, 

 presphenoidal part, and a posterior, postsphenoidal part. 

 The presphenoidal part of the bone contains a median ele- 

 ment, the presphenoid, and two lateral elements, the orbito- 

 sphenoids, one on each side of the head. The postsphenoidal 

 part of the bone contains a median element, the basisphenoid, 

 and three lateral elements on each side, the alisphenoid, the 

 sphenotic, and the internal pterygoid plate, the latter being 

 developed from one of the appendages of the skull, the palato- 

 pterygoid bone, and hence not a part of the cranium proper. 



The presphenoid first appears in man, according to Sutton 

 (No. 29, p. 581), as a pair of nuclei on the inner sides of the 

 optic foramina. These nuclei lie on the deep aspect of 

 the perichondrium, and do not involve the subjacent cartilage 



