THE CONNECTIVE TISSUES AND THE SKELETAL SYSTEM. 



197 



The temporal is also a composite bone, the petrous and mastoid parts 

 and the styloid process being of intracartilaginous origin, while the temporal 

 squama and the tympanic part are of intramembranous origin. During the 

 eighth week of fcetal life a center of ossification appears in the membrane in the 

 temporal region, and the bone formed from this center subsequently unites 

 with the petrous part and becomes the temporal squama. Another center ap- 

 pears in the membrane to the outer side of the periotic capsule and produces a 

 ring of bone around the external auditory meatus, which fuses with the petrous 



Parietal 



Occipital 



fontanelle 



Occipital ~ 



Mastoid - 

 fontanelle 



Occipital 



Petrous 



Occipital 



Tympanic 



Styloid process 



Stylohyoid lig. . 



Hyoid (greater horn) . 



Cricoid 



Mandible 



Meckel's cartilage 

 Hyoid (lesser horn) 



Thyreoid 



FIG. 177. Diagram of skull of new-born child. Combined from McMurrich and Kollmann. 

 White areas represent bones of intramembranous origin; dotted areas represent bones (not derived 

 from branchial arches) of intracartilaginous origin; black areas represent derivatives of 

 branchial arches. 



part and forms the tympanic part of the adult bone. It gives attachment at its 

 inner border to the tympanic membrane. While the union of the different 

 parts begins during foetal life, it is usually completed after birth. 



The sphenoid bone is also composed of parts which have different 

 origins. The body, small wings and large wings are of intracartilaginous 

 origin, the pterygoid process of intramembranous origin. About the eighth 

 week of development a center of ossification appears in the mesenchyme in the 

 lateral wall of the posterior part of the nasal cavity and gives rise to the medial 

 pterygoid lamina. On the tip of the latter a small piece of cartilage appears in 



