no 



THE SKELETON 



the two are usually separated by the orbital plate of the zygomatic, and on the latter are seen 

 the orifices of the zygomatico-temporal and zygomatico-facial canals, which traverse the 

 zygomatic bone. The commencement of the zygomatico-temporal canal is sometimes seen in 

 the spheno-zygomatic suture connecting the sphenoid and zygomatic bones. 



The medial wall, narrow and nearly vertical, is formed from before backward by the 

 frontal process of the maxilla, the lacrimal, the lamina papyracea of the ethmoid, and the 

 body of the sphenoid. At the junction of the medial wall with the roof, and in the suture 

 between the ethmoid and frontal, are seen the orifices of the anterior and posterior ethmoidal 

 canals, the anterior, transmitting the anterior ethmoidal vessels and nerve; and the posterior, 

 the posterior vessels and nerve. Anteriorly is the lacrimal groove for the lacrimal sac, and 

 behind this the lacrimal crest, from which the tensor tarsi arises. The medial wall, which is 

 the smallest of the four, is traversed by tliree vertical sutm'es: — one between the frontal process 

 of the maxilla and the lacrimal, a second between lacrimal and lamina papyracea, and a third 

 between the lamina papyracea and the sphenoid. Occasionally the sphenoidal concha appears 

 in the orbit between the ethmoid and the body of the sphenoid. 



The apex of each orbit corresponds to the optic foramen, a circular orifice which transmits 

 the optic nerve and ophthalmic artery. The base or circumference is quadrilateral in form 

 and is bounded by the frontal bone above, the frontal process of the maxilla and the medial 

 angular process of the frontal on the medial side, the zygomatic bone and the zygomatic process 

 of the frontal on the lateral side, and by the zygomatic and the body of the maxilla below. 

 The following points may also be noted: — The suture between the zygomatic process of the 

 frontal bone and the zygomatic; the supra-orbital notch (sometimes a complete foramen); 

 the suture between the frontal bone and the frontal process of the maxilla; and in the lower 

 segment, the zygomatico-maxiUary suture. 



The orbit communicates with the cranial cavity by the optic foramen and superior orbital 

 fissure; with the nasal fossa, by means of the naso-lacrimal canal; with the zygomatic and 

 ptery go-palatine fossae, by the inferior orbital fissure. In addition to these large openings, the 

 orbit has five other foramina — the infra-orbital, zygomatico-orbital, and the anterior and 

 posterior ethmoidal canals — opening into it or leading from it. 



The following muscles arise within the orbit: — the /o!/r recti, the superior oblique, and 

 levator palpebrcB superioris, near the apex; the inferior oblique on the floor of the orbit lateral 

 to the naso-lacrimal canal; and the tensor tarsi from the lacrimal creBt. The margins of the 

 inferior orbital fissure give attachment to the orbitalis muscle. 



THE NASAL FOSS^ 



The nasal fossae (figs. 135, 136) are two irregular cavities situated on each 

 side of a median vertical septum. They open in front by the piriform aperture 

 and communicate behind with the pharynx by the choanse. They are somewhat 



Fig. 135. 



-Section through the Nasal Fossa to show the Septum. 

 Septum looking toward Right Nasal Fossa. 



Left Half, with 



Crest of sphenoid r^;^ — 



Groove for naso-palatine nerve 



Crest of palate bone. 

 Spine of palate bone 



Frontal spine 



Crest of maxilla 



oblong in transverse section, and extend vertically from the anterior part of the 

 base of the cranium above to the superior surface of the hard i)alate below. 

 Their transverse extent is very limited, especially in the upper part. Each fossa 

 presents for examination a roof, floor, medial and lateral walls, and communicates 

 with the sinuses of the frontal, sphenoid, maxilla, and ethmoid bones. 



I 



