44 ATLAS AND TEXT-BOOK OF HUMAN ANATOMY. 



Fig. 46. — The skull seen from above (3-). 

 X = foramen parictalc. 



Fig. 47.— The inner surface of the roof of the skull (calvarium) (£). 



The posterior margin of the round foramen magnum, situated in the middle of the posterior 

 fossa, is formed by the squamous portion of the occipital, which exhibits, below the transverse 

 groove, two concave depressions, the inferior occipital fossa, which are separated by a median 

 ridge, the internal occipital crest. 



THE SUPERIOR ASPECT OF THE SKULL. 

 The superior aspect of the skull (Fig. 46} is much less complicated. It shows only four 

 bones, the vertical portion of the frontal, the large surfaces of the two parietals, and the apex 

 of the squamous portion of the occipital. The visible sutures are the coronal suture, the sagittal 

 suture, separating the parietal bones throughout their entire length, and the lambdoid suture, 

 which forms an obtuse angle with the sagittal suture. In the parietal bone, on either side of 

 the sagittal suture and at about the junction of the third and fourth quarters, there is an orifice, 

 the parietal foramen, and the foreshortened temporal line can also be seen. 



THE INNER ASPECT OF THE CRANIAL VAULT OR CALVARIA. 



The inner surface of the cranial vault (Fig. 47) corresponds to the outer surface with slight 

 differences. It presents the same bones, frontal, parietal, and occipital, and the same sutures, 

 the coronal, sagittal, and lambdoid. Upon the inner surface of the sagittal suture we find a 

 shallow groove, the sagittal groove, which commences at the crest of the frontal bone and passes 

 backward over the parietal to the occipital bone. The cerebral surfaces of all the bones of the 

 cranial vault show vascular grooves, the sulci arteriosi; the}- are found in greatest numbers 

 upon the parietal bone and, next in frequency, upon the frontal bone. Small inconstant depres- 

 sions, often of inconsiderable depth and situated particularly along the sagittal suture, are desig- 

 nated as the joveola granular es or Pacchionian depressions. 



THE BONES OF THE SKULL. 



After this consideration of the skull as a whole we turn to the description of the individual 

 bones of the skull. These may be divided into two groups: (1) the bones of the cranium (cranium 

 cerebrale), and (2) the bones of the face (cranium viscerate). The cranial bones are the occipital 

 bone, the sphenoid bone, the two temporal bones, the two parietal bones, the frontal bone, and 

 the ethmoid bone. The facial bones arc the nasal bones, the lachrymal bones, the vomer, the 

 inferior turbinated bones (concha nasales inferiorcs), the maxilla, the palate bones, the zygomatic 

 bones, the mandible, and the hyoid bone. 



The bones of the skull may also be classified according to the method of their development (see page 21), and from 

 this standpoint they arc quite heterogeneous structures; some of them, such as those of the base of the skull, are devel- 

 oped in the primordial cartilaginous cranium, some are portions of the visceral skeleton, and some are so-called covering 



