THE BONES OF THE HEAD 



i6t 



The basal Cartilage is conveniently di\-idcd, for purposes of development, 

 into three regional parts, which, in order from behind forwcirds, are as follows: 

 (i) bcisi-occipital, (2) basisphenoid, and (3) ethmoidal. In addition to these 

 three parts there are the two periotic cartilaginous capsules, right and left. 



The basi-occipital cartilage gives rise to the following parts of the occipital 

 bone— namely, (i) the basi-occipital, or basilar process; (2) the exoccipitals, or 

 condylar portions; and (3) the supra-occipital, or lower division of the tabular 

 portion. 



The basisphenoid cartilage gives rise to the following parts of the sphenoid 

 bone — namely: (i) the basisphenoid, or posterior part of the body, inclusive 

 of the sella turcica; (2) the aJisphenoids, or great wings; and (3) the external 

 pter^'goid plates. 



The ethmoidal cartilage gives rise to osseous parts as follows: the posterior 

 portion gives rise to (i) the presphenoid, or anterior part of the body of the 

 sphenoid, and (2) the orbito-sphenoids, or small wings of the sphenoid. 



B m npr 



m n pr 



npr 



Fig. 91. — Head of an Embryo (His). 



A, View from above. — B. View showng roof of mouth after removal of the 

 Mandible. /«/»', Fronto-Nasal Process; mnpr. Mesial Nasal Process, 

 terminating in Globular Process ; Inpr. Lateral Nasal Process | 

 mx. Maxillary Process; mn. Mandibular Arch; hy, Hyoid Arch. The 

 X in B indicates the Nasal Lamina. 



The anterior portion gives rise mesiaUy to the mesethmoid, or crista galli, 

 and perpendicular plate of the ethmoid, as well as to the septal cartilage of 

 of the nose. It is also prolonged anteriorly at its centre into the fronto- 

 nasal process, of which it forms the core. 



Each lateral part of the anterior portion of the ethmoidal cartilage gives 

 rise to the foUow-ing parts— nam ety, (i) the ethmo-turbinal, or lateral mass 

 of the ethmoid, inclusive of the superior and middle conchae of the ethmoid ; 

 (2) the inferior concha ; and (3) the sphenoidal turbinate bone of one side. 



Each periotic cartilagiooos capsule gives rise to the greater part of the 

 petro-mastoid portion of the temporal bone. 



The ethmoidal division of the basal cartilage undergoes considerable modi- 

 fication. It spreads out laterally, so, that it forms a broad plate. On either 

 side in the region of each olfactory pit it assumes a deeply-curved crescentic 

 outline, and forms the cartilaginous nasal capsule, this being the part which 

 gives rise on either side to the ethmo-turbinal. inferior concha, and sphenoidal 



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