116 



VERTEBRATA. 



skull* is developed partly by ossifications in the cartilaginous 

 capsule or by ossifications proceeding from the membranous peri- 

 chondrium ; partly by the addition of membrane bones, which 

 gradually supplant the cartilaginous parts. 



Segmentation of the skull. It is only when the cranial capsule is 

 bony that any comparison can be instituted between the arrangement 

 of the hard parts of the skull and that of the parts of a vertebra : 

 this comparison has led to the view that the skull is composed of 

 three or four vertebra? or segments. These are from behind forwards, 

 the occipital, parietal, frontal and ethmoid segments. Each such 

 segment, according to the vertebral theory of (P. Frank) Goethe and 



Ql 



FIG. 574. Lateral view of a goat's skull ; O/, exoccipital bone; C, condyle ; Os, supra- 

 occipital; Sq, squamosal ; Ty, tympanic; Pe, petrosal ; Pm, paramastoicl process; Pa, 

 parietal; Fr, frontal, Lti, lachrymal ; -ZV, nasal ; Fo, optic foramen ; MX, maxilla; Jiux, 

 inter-maxilla (pre-maxilla) ; Jn, jugal ; Pa/, palatine ; Ft, pterygoicl. 



Oken, is supposed to consist of a basal part corresponding to the body 

 of the vertebra, and of a neural arch formed of two lateral pieces and 

 a median dorsal piece (spinous process) (fig. 574). According to this 

 theory the basi-occipital bone would correspond to the body of the 

 vertebra, the two exoccipitals to the lateral parts of the neural arch, 

 and the supra-Occipital to the dorsal median parts or spinous 

 process. The bones of the middle or parietal region of the skull 

 consist of a basal bone, the , basisphenoid, two lateral bones, the 

 alisphenoids and two dorsal bones, the parietals ; the two latter are 

 membrane bones, and complete the arch dorsally. The bones of the 



* Compare especially Eeichert and Kolliker. Huxley, Parker etc. 



