in.] THE CRANIAL SKELETON. 



79 



and which is called the temporal bone. Above the mastoid 

 it articulates on each side with one of the two great plate- 

 bones which roof the skull at the top and sides, and which 

 ire called the parietals. 



In a new-born child the occipital bone consists of four 

 parts : (i), a median piece in front of the foramen magnum, 

 and which, as contributing to form the base of the skull, is 

 called "basilar;" (2 and 3), two "lateral" pieces, one 'on 

 each side of the foramen magnum, each supporting a con- 

 dyle, and pierced for the hypoglossal nerve ; (4), a large 

 median plate placed above the foramen magnum, and there- 

 fore called a " supra-occipital? and which shows traces of its 

 origin from more than one centre of ossification. 



3. The PARIETAL bone is very large, and is connected 

 with its fellow of the opposite side by the sagittal suture, with 

 the occipital behind by the lambdoidal suture, anteriorly 

 with the frontal by the coronal suture, and below with the 

 temporal bone by a suture which is called squamous, 

 because the margins of the bones it joins are so bevelled 

 off that the temporal lies on the parietal like a scale. 



The parietal arises from but one centre of ossification. 



4. The remaining bone of the skull-roof is the FRONTAL, 

 which, single in the adult, is at birth divided into two parts 

 by a line of separation which continues onwards the median 

 separation between the contiguous parietals. 



The anterior end of this bone is, as it were, bent sharply 

 backwards on each side to form two plates which roof the 

 bony orbits, while between these plates a space is left filled up 

 naturally by the bone forming the summit of the nasal cavity, 

 and called the ethmoid. Above the margins of each orbit are 

 slight transverse curved prominences, called the superciliary 

 and supra-orbital ridges, while each margin itself runs out into 

 what is named the external angular process, at each outer 

 inferior angle of the frontal bone, and joins the bone of the 

 cheek, or malar. Besides the unions just mentioned, the 

 frontal unites with bones to be hereafter described, namely 

 the sphenoid, nasals, lachrymals, and maxillaries. 



5. On each side of the skull we find an exceedingly com- 

 plex bone called the TEMPORAL. (See Figs. 83, 89, 90, and 91.) 



Part of it, as already mentioned, articulates with the 

 parietal by a squamous suture, and it is this part which forms 

 the hinder part of the zygoma and the articular " glenoid " 

 surface for the lower jaw. 



A portion of bone which bounds the external opening of the 



