180 



OSTEOLOGY 





by the superior nuchal lines of the occipital; and laterally by the alveolar arch, 

 the lower border of the zygomatic bone, the zygomatic arch and an imaginary 

 line extending from it to the mastoid process and extremity of the superior nuchal 

 line of the occipital. It is formed by the palatine processes of the maxillae and 

 palatine bones, the vomer, the pterygoid processes, the under surfaces of the 

 great wings, spinous processes, and part of the body of the sphenoid, the under 

 surfaces of the squamae and mastoid and petrous portions of the temporals, and 

 the under surface of the occipital bone. The anterior part or hard palate projects 

 below the level of the rest of the surface, and is bounded in front and laterally 

 by the alveolar arch containing the sixteen teeth of the maxillae. Immediately 

 behind the incisor teeth is the incisive foramen. In this foramen are two lateral 

 apertures, the openings of the incisive canals (foramina of Stenson) which transmit 

 the anterior branches of the descending palatine vessels, and the nasopalatine 

 nerves. Occasionally two additional canals are present in the incisive foramen; 

 they are termed the foramina of Scarpa and are situated in the middle line; when 

 present they transmit the nasopalatine nerves. The vault of the hard palate 

 is concave, uneven, perforated by numerous foramina, marked by depressions for 

 the palatine glands, and traversed by a crucial suture formed by the junction of the 

 four bones of which it is composed. In the young skull a suture may be seen ex- 

 tending on either side from the incisive foramen to the interval between the lateral 

 incisor and canine teeth, and marking off the os incisivum or premaxillary bone. 

 At either posterior angle of the hard palate is the greater palatine foramen, for the 

 transmission of the descending palatine vessels and anterior palatine nerve; and 

 running forw r ard and medialward from it a groove, for the same vessels and nerve. 

 Behind the posterior palatine foramen is the pyramidal process of the palatine bone, 

 perforated by one or more lesser palatine foramina, and marked by the commence- 

 ment of a transverse ridge, for the attachment of the tendinous expansion of the 

 Tensor veli palatini. Projecting backward from the center of the posterior border 

 of the hard palate is the posterior nasal spine, for the attachment of the Musculus 

 uvulae. Behind and above the hard palate are the choanae, measuring about 

 2.5 cm. in their vertical and 1.25 cm. in their transverse diameters. They are 

 separated from one another by the vomer, and each is bounded above by the body 

 of the sphenoid, below by the horizontal part of the palatine bone, and laterally 

 by the medial pterygoid plate of the sphenoid. At the superior border of the 

 vomer may be seen the expanded alae of this bone, receiving between them the ros- 

 trum of the sphenoid. Near the lateral margins of the alae of the vomer, at the 

 roots of the pterygoid processes, are the pharyngeal canals. The pterygoid process 

 presents near its base the pterygoid canal, for the transmission of a nerve and artery. 

 The medial pterygoid plate is long and narrow ; on the lateral side of its base is the 

 scaphoid fossa, for the origin of the Tensor veli palatini, and at its lower extremity 

 the hamulus, around which the tendon of this muscle turns. The lateral pterygoid 

 plate is broad; its lateral surface forms the medial boundary of the infratemporal 

 fossa, and affords attachment to the Pterygoideus externus. 



Behind the nasal cavities is the basil ar portion of the occipital bone, presenting 

 near its center the pharyngeal tubercle for the attachment of the fibrous raphe 

 of the pharynx, with depressions on either side for the insertions of the Rectus 

 capitis anterior and Longus capitis. At the base of the lateral pterygoid plate 

 is the foramen ovale, for the transmission of the mandibular nerve, the accessory 

 meningeal artery, and sometimes the lesser superficial petrosal nerve ; behind this are 

 the foramen spinosum which transmits the middle meningeal vessels, and the promi- 

 nent spina angularis (sphenoidal spine), which gives attachment to the spheno- 

 mandibular ligament and the Tensor veli palatini. Lateral to the spina angularis 

 is the mandibular fossa, divided into two parts by the petrotympanic fissure; the 

 anterior portion, concave, smooth, bounded in front by the articular tubercle, 



