168 



ON THE STRUCTURE OF THE SKULL. 



rated by a plate of cartilage, which corresponds to a certain 

 extent with the crista galli of the human skull. 



Fig. 69. 



<\ 



Fig. 69. — Side and upper views of a Pike's skull (after Agassiz). — a, the articular facet 

 for the hyomandibular bone; x, the " parasphenoid ;" y, the true basi-sphenoid ; 

 z, the alisphenoid. 



Immediately in front of the pituitary fossa a thin plate-like 

 ossification, y, is developed in the cartilage, and this plate sends 

 off backwards and a little upwards, upon each side, a process 

 which is connected posteriorly with the cranial floor. These 

 two processes consequently lie at the sides of the pituitary 

 fossa, and the "Y-shaped bone," as it has been well termed, 

 thus furnishes part of the front and side walls of that fossa. 



The next ossification to be noted in the cranio-facial axis of 

 the Pike is the great bone x (Figs. 66 to 69), which stretches, 

 like a splint, along the greater part of the length of the base of 

 the skull. 



The lower face of the hinder half of this bone is free, while 

 that of its front half is covered by the bone, Vo. The upper 

 face of its hinder half articulates, at first, with the lower surface 

 of B.O., but is then free for some distance, forming the floor of 

 the canal for the orbital muscles, and articulates by expanded 

 aliform processes of its sides with the lateral walls of that canal- 

 At the front part of the canal it exhibits the elevation which 

 forms the floor of the pituitary fossa, and then, depressed at the 

 sides, but exhibiting a median superior ridge, it underlies \\u- 

 inter-orbital and ethmoidal cartilages. 



