THE SKULL IN GENERAL. 71 



In the temporal bones 



Ossification of the squamous part appears in the 7th or 8th week. 



Ossification of the petro-mastoid part appears in the 4th month. 



Ossification of the ossicula auditoria appears in the 4th month. 



Ossification of the tympanic ring appears in the 3rd month. 



Ossification of the styloid process appears after puberty. 



The tympanic ring unites with the squamous part at birth. 



The squamous and petro-mastoid parts unite in the 1st year. 

 In the sphenoid bone 



Ossification of the great wings appears in the 8th week. 



Ossification of the posterior part of the body appears in the 8th or 9th week. 



Ossification of the internal pterygoid processes appears in the 4th month. 



Ossification of the anterior part of the body, including the small wings, appears 

 in the 8th or 9th week. 



Ossification of the sphenoidal spongy bones appears about the time of birth. 



The centres of the posterior part of the body unite in the 4th month. 



The internal and external pterygoid processes unite in the 5th or 6th month. 



The anterior and posterior parts of the body unite in the 8th month. 



The body and great wings unite in the 1st year. 



The sphenoidal spongy bones and the body unite about the age of puberty. 

 In the ethmoid bone 



Ossification of the lateral masses appears in the 4th or 5th month. 



Ossification of the vertical and cribriform plates appears in the 1st year. 

 In the superior maxillary bones ossification appears in the 6th or 7th week. 

 In the palate, vomer, nasal, and malar bones ossification appears in the 7th or 



8th week. 



In the lachrymal bones ossification appears in the 8th week. 

 In the inferior turbinated bones ossification appears in the 5th month. 

 In the inferior maxillary bone ossification appears in the 6th week. 



The two parts of the inferior maxillary bone unite in the 1st year. 

 In the hyoid bone 



Ossification of the body and great cornua appears before birth. 



Ossification of the small cornua appears in the 1st year. 



THE VERTEBRAL THEORY OP THE SKULL. 



The idea that the skull is composed of a series of vertebrae, whose arches are expanded 

 and united to enclose and protect the encephalon, appears to have originated with 

 Goethe in 1791, but occurred independently to Oken, and was first published by him 

 in 1 807. Since then many conflicting theories have been brought forward on the subject 

 by different anatomists, who have estimated the cranial vertebrae at numbers varying 

 from three to seven ; while by others the idea has been entirely rejected, and even 

 the possibility of referring the bones of the skull to distinct segments denied. Some 

 of the facts in favour of the vertebral theory are sufficiently manifest. Thus, the 

 basilar process of the occipital bone, and the mesial parts of the post-sphenoid and 

 pre-sphenoid bones, lie in series with and bear considerable resemblance to the centra 

 or bodies of vertebrae, as is seen particularly in those animals in which the pre- 

 sphenoid and post-sphenoid bones remain distinct : the visceral arches of the embryo 

 likewise form a series : in the roof of the skull a certain degree of repetition of parts 

 from behind forwards is also visible, especially in some of the lower animals : the 

 mode of formation of the head and of the trunk is almost the same up to the time 

 when the primordial vertebrae appear in the latter : and lastly, the general resem- 

 blance of the occipital bone to a vertebra is admitted by all. On the other hand, it 

 must be allowed that there is no original division of the cartilaginous basis of the 

 cranium ; in that part of it which lies in front of the sphenoid bone, and to which 

 the chorda dorealis does not penetrate, it is not easy to trace a resemblance to vertebral 

 form ; and in the face it is still more difficult to demonstrate in the several parts a 

 definite arrangement of visceral or costal arches. Deterred by the differences of opinion 

 with respect to the number of cranial segments and the bones which belong to each, 

 some may be inclined to set aside the discussion entirely, but we must not too rashly 

 decide against the existence of such segmentation, nor forget that some correspondence 



