176 OSTEOLOGY. 



zygomatic arch, though the student must bear in mind the fact that when the 

 mandible is in position the lateral limits of the space are very much reduced (p. 168). 

 The inferior surface of the great wing of the sphenoid is here V-shaped. The 

 angle corresponds to the spine, the lateral limb to the spheno-squamosal suture, 

 whilst the medial limb corresponds to a narrow cleft, the fissura spheno-petrosa, 

 which separates it from the petrous portion of the temporal bone, to which it is 

 united in the recent condition by a synchondrosis. Along the line of this latter 

 fissure the edges of the adjacent bones (sphenoid and petrous part of the temporal) are 

 bevelled so as to form a groove, which extends from the root of the medial pterygoid 

 lamina medially, to the medial side of the base of the angular spine laterally, where 

 the groove ends by entering an osseous canal. In the groove (sulcus tubae auditivae) 

 the cartilaginous part of the auditory tube is lodged, whilst the osseous canal 

 includes the bony part of the same tube, together with the tensor tympani muscle, 

 which is lodged in a separate compartment immediately above it. The anterior 

 extremity of the cartilaginous part of the auditory tube is supported by the 

 posterior edge of the medial pterygoid lamina, which is often notched for its recep- 

 tion. Between the root of the lateral pterygoid lamina and the angular spine there 

 are two foramina which lie immediately in front of the sulcus tubse auditivse. 

 Of these the larger and anterior is the foramen ovale, through which pass the! 

 motor root, and mandibular division of the trigeminal nerve, together with the| 

 accessory meningeal artery. The smaller, which, from its position immediately in 

 front of the angular spine, is called the foramen spinosum, transmits the middle 

 meningeal artery and vein, and sympathetic plexus surrounding the artery. Th< 

 lesser superficial petrosal nerve here passes through the base of the skull to join 

 the otic ganglion either through a small foramen (canalis innominatus) placec 

 between the foramen ovale and the foramen spinosum, or through the foramen 

 ovale or through the spheno-petrosal fissure. The position of the suture between 

 the basi-occipital and basi-sphenoid corresponds to a line connecting the tips of th( 

 pterygoid .tubercles at the root of the medial pterygoid laminae. 



Occasionally in the centre of this line there is a small pit with a foramen leading from it. Tlii 

 probably represents the lower end of the cranio-pharyngeal canal. 



The inferior surface of the basilar part of the occipital bone (basi-occipital 

 stretches between the body of the sphenoid in front and the anterior margin o 

 the foramen magnum behind ; projecting from its centre is a slight elevation, tht 

 pharyngeal tubercle, to which the pharyngeal raphe, together with the centra 

 part of the anterior atlanto-occipital membrane, is attached. It should be noted 

 that when the atlas is in position the pharyngeal tubercle lies in line with th( 

 tubercle on the anterior arch of that bone. Curving laterally and backward 

 from the pharyngeal tubercle, on either side, is an irregular ridge (crista muscularis) 

 in front and behind which are attached the longus capitis and rectus capitis anterio 

 muscles. On either side of the basi-occipital, in front, there is an irregular opening 

 of variable size ; this is placed between the root of the pterygoid process anteriorly 

 the apex of the petrous portion of the temporal bone laterally, and the latera 

 edge of the basi-occipital and basi-sphenoid medially. It is called the foramei 

 lacerum. Opening into it in front, just lateral to the pterygoid tubercle, is th< 

 pterygoid canal, whilst, in correspondence with the apex of the petrous part of th < 

 temporal, the large orifice of the carotid canal may be seen entering it behind an< 

 from the lateral side. In the recent condition the lower part of the foramen lacerur 

 is occupied by fibro-cartilage, over the upper surface of which the internal caroti* 

 artery and greater superficial petrosal nerve pass to reach their respective foraminr 

 whilst a small meningeal branch of the ascending pharyngeal artery occasional! 

 enters the cranium through it. Leading laterally from the foramen lacerum in th 

 direction of the angular spine of the sphenoid is the spheno-petrosal fissure, whic 

 lies at the bottom of the sulcus tubae auditivae, and disappears from view within th 

 bony part of the auditory tube. Passing backwards from the foramen lacerum thei 

 is a fissure between the lateral side of the basi-occipital and the posterior an 

 medial border of the petrous part of the temporal bone. This, which is called tt ! 

 petro-occipital fissure, opens posteriorly into the jugular foramen. In the recer 



