126 THE SKELETON 



The ethmoidal canals. — These commence in the suture between the lamina papyracea and 

 the frontal bone, and traverse the space between the upper surface of the lateral mass of the 

 ethmoid and the horizontal plate of the frontal, to emerge on the cribriform plate; they are 

 situated outside the dura mater. The anterior foramen transmits the anterior ethmoidal 

 branch of the ophthalmic, which subsequently gains the nasal cavity by passing through the 

 ethmoidal fissure by the side of the crista galli 



The infra-orbital canal indicates the line of confluence of the maxillary and malar centres 

 of the maxilla; occasionally it is completed by the zygomatic; rarely it is incomplete above, 

 and communicates by a narrow fissure with the orbit. It lodges the infra-orbital nerve and 

 artery. 



The zygomatico -temporal foramen is situated in the suture between the zygomatic and 

 the greater wing of the sphenoid (ali-sphenoid) ; it transmits the temporal branch of the zygo- 

 matic nerve and a branch of the lacrimal artery. In the adult this foramen may be wholly 

 confined to the zygomatic bone. 



The zygomatico -facial canals traverse the zygomatic bone, and indicate the line of con- 

 fluence of the two chief centres for this bone. The facial twigs of the zygomatic nerve issue 

 from them accompanied by arterial twigs. 



The spheno-palatine foramen is a deep groove between the orbital and sphenoidal pro- 

 cesses of the palate bone, converted into a foramen by the sphenoidal concha. It is traversed 

 by the naso-palatine nerve and artery as they enter the nasal from the pterygo-palatine fossa. 



Scarpa's foramina are two minute openings in the meso-palatine suture where it is in 

 relation with the incisive fossa. They are traversed by the naso-palatine nerves. 



The pharyngeal foramen is situated between the sphenoidal process of the palate bone, 

 the medial pterygoid plate of the sphenoid, and the sphenoidal concha. The pharyngeal 

 branch of the spheno-palatine ganglion and a branch of the spheno-palatine artery pass 

 through it. 



The pterygoid (Vidian) canal is trumpet-shaped: the narrower end is situated in the foramen 

 lacerum; the broader orifice opens on the posterior wall of the pteryo-palatine fossa. The canal 

 is 10 mm. long; in the foetal skull it is a chink between the base of the medial pterygoid plate, 

 the aU-sphenoid, and the lingula of the sphenoid. The canal is traversed by the Vidian branch 

 of the spheno-palatine ganglion and the Vidian artery. 



The posterior (greater) palatine canal is a passage left between the maxilla, the vertical 

 plate and tuberosity of the palate bone and the medial pterygoid plate; it commences on the 

 hard palate by the greater palatine foramen. The descending palatine nerve and artery trav- 

 erse this canal. Several foramina open from it. In the suture between the vertical plate of the 

 palate bone and the maxilla, two small openings allow minute nerves to issue for the middle and 

 inferior nasal conchse. In the fissm-es between the tuberosities of the palate and maxillae, and 

 the pterygoid plates, the posterior and middle palatine nerves issue. These are sometimes called 

 the posterior and middle (smaller) palatine canals. 



The mandibular or inferior dental canal runs in the mandible between the dentary and 

 Meckel's cartilage of the mandible. The posterior orifice of the canal is the mandibular (infe- 

 rior dental) foramen; the anterior orifice is the mental foramen. The inferior alveolar nerve 

 and artery enter the canal at its posterior orifice; the mental foramen allows the mental nerve 

 to escape from the canal accompanied by the mental artery. 



Foramina transmitting the facial nerve and its branches. — The main trunk of the facial 

 enters the internal auditory meatus and traverses the facial canal. In the early embryo the 

 nerve lies on the petrosal, and is not covered in with bone until the fifth month of foetal life. 

 The terminal orifice, the stylo-mastoid foramen, is situated between the tympanic, tympano- 

 hyal, and epiotic elements of the complex temporal bone. 



The 'iter chordae posterius' is a chink between the squamosal and the tympanic elements, 

 and allows the chorda tympani nerve to enter the tympanum. The fissure of exit for this nerve 

 is the subdivision of the petro-tympanic fissure termed the canal of Huguier, or 'iter chordae 

 anterius.' The petro-tympanic fissure lies between the tympanic plate and the squamosal. 

 It transmits the tympanic branch of the internal maxillary artery, and lodges the anterior proc- 

 ess of the malleus. 



The inferior orbital (spheno-maxillary) fi.ssure is situated between the posterior border 

 of the orbital plate of the maxilla and a smooth ridge on the orbital surface of the great wing 

 of the sphenoid. It transmits the superior maxillary division (second) of the fifth nerve, the 

 zygomatic nerve, branches of the spheno-palatine ganglion to the orbit, and a communicating 

 vein from the ophthalmic to the pterygoid plexus. 



C. THE THORAX 



The thorax is a bony cage formed by the thoracic vertebrae already described, 

 tlie ribs with their costal cartilages, and the sternum. 



THE RIBS 



The ribs [costs] (figs. 154, 155) twelve in number on each side, constitute a 

 series of narrow, flattened bones, extending from the sides of the thoracic vertebrae 

 toward the median line on the anterior aspect of the trunk. The anterior ends 

 of the first seven pairs are connected, by means of their costal cartilages, with the 

 sides of the sternum, and on this account the first seven ribs on each side are 



I 



