INTERIOR OF THE SKULL 



81 



maxillary, and malo-maxillarv. The small sutures visil)lc in tlic orl)it have l)eeu 



already mentioned in dcscrihing that eavity. 



The f()ll()win<f points are seen in an anterior view of the eranium: — 

 Tlie glabella, a smooth space hetween tlie converging superciliary ridges. 

 The ophryon is the most anterior point of the metopic suture. 



Fig. 89. — Thk Postkriok Nares. 



pterygo-palatine canals 



FORAMEN OVALE 



SCAPHOID FOSSA 



PTERYGOID FOSSA 

 EXTERNAL PTERYGOID PLATE 



TUBEROSITY OF PALATE BONE 



INTERNAL PTERYGOID PLATE 



HAMULAR PROCESS 



SPINE OF PALATE OR POSTERIOR 

 NASAL SPINE 



Tlie nasion is the central point of the transverse suture. 



The subnasal point is the middle of the inferior border of the anterior nasal 

 a{)erture at tlie base of the nasal spine. 



The alveolar point is the centre of the anterior margin of the upper alveolar 

 arch. 



THE INTERIOR OF THE SKULL 



In order to study the interior of the skull it is necessary to make sections in 

 three directions, — sagittal, coronal, and horizontal. This enables the student to 

 examine the various points with facility, and displays the great pro[)ortion the 

 brain cavity bears to the rest of the skull. The sagittal section should be made 

 slightly to one side of the median line in order to i)reserve the nasal septum. The 

 black line (fig. 90) drawn from the basion (anterior margin of the foramen mag- 

 num) to the gonion (the anterior extremity of the sphenoid) represents the basi- 

 cranial axis ; whilst the line drawn from the gonion to the subnasal point lies 

 in the basi-facial axis. These two axes form an angle termed tlie cranio-facial, 

 which is useful in making comparative measurements of crania. A line prolonged 

 vertically upwards from the basion will strike the bregma. This is the basi- 

 bregmatic axis, and gives the greatest height of the cranial cavity. A line drawn 

 from the ophryon to the occipital point indicates the greatest length of the 

 cranium. 



Near its middle, the cranial cavity is encroached upon by the ]ietrosal; the 

 walls are (channelled vertically by narrow grooves for the middle and small meningeal 

 arteries, and towards the base and at the vertex broader furrows are found for the 

 venous sinuses. 



The coronal section is most instructive when made in the basi-bregmatic axis. 

 The section will pass through the petrosal in such a way as to traverse the two 

 external auditory passages and expose the tympanum and vestibule, and will also 

 partially traverse the internal auditory meatuses. Such a section will divide the 

 parietal bones slightly posterior to "the parietal eminences, and a hue drawn 

 transversely across the section at the miil-])oint Avill give the greatest transverse 

 6 



