66 SPECIAL ANATOMY. 



d. M. orbitalis internus, by nasal process of super. Maxillary and internal 

 angular process of Frontal bone ; immediately behind is the little Lacrymal 

 bone. The circumference is narrower than the cavity behind it. 



2. The Walls, covered with periosteum, Periorbita, formed of seven bones. 



a. Superior, the roof, formed before by the frontal, behind by the lesser 

 wing of the Sphenoid bone, presents : an external angle, fove.a lacrymal., for 

 the lacrymal gland ,- an internal, fovea, s. Spina Trochlearis, for the tendon of 

 the m. obliq. superior ; posteriorly, the suture between the Frontal and Sphe- 

 noid bones. 



b. Inferior, floor, inclined outwards and downwards, formed by marg. orbi- 

 tale of the malar, fades orbit, of the upper jaw, and behind by the Proc. orbi- 

 tal, of the Palate bone; with, Canal, infraorbitalis , bounded externally by the 

 fissur. orbital, inferior. 



c. External wall, formed by the great wing of the Sphenoid and the Malar 

 bones, with: Fissura orbit ale inferior be\ow,jfissura orbit, superior behind, and 

 an oblique groove upon the malar bone leading to the superior or posterior 

 malar canal, for the temporal twigs of the nerve. 



d. Internal, formed by Lacrymal, Ethmoid, and the small wing of the 

 Sphenoid bone. On this wall there are two vertical sutures; Fossa lacry- 

 malis, and entrance to the Canalis lacrymalis, Foram. Ethmoidalia, Spina s. 

 fovea Trochlearis, for the cartilaginous loop through which the tendon of the 

 m. obliq. superior passes. 



3. Apex, above, and internal, foramen opticum; below, the Fissura supra 

 and infra orbitalis and fossa Spheno-maxillaris meet together. 



Connected with: 1. The cranial cavity, by iheforam. opticum, 

 Fissur. orbital, superior zndforam. ethmoid, post. 



2. The nasal cavity, by the for am. ethmoidalis ant. and ca- 

 nalis lacrymalis. 



3. The Temporal and Pterygo-palatine fossa by the fissur. 

 orbital, inferior and canalis zygomat. superior s. posterior. 



69. 2. Cavitas nasi, nasal cavity, 



consists of two principal cavities lying close together, and sepa- 

 rated by a septum or partition, situated between and below the 

 two orbits, and bounded above by the horizontal plate of the 

 ethmoid ; below, by the united superior maxillary and palate 

 bones, open before and behind, and covered with a mucous mem- 

 brane, Membr.Schneideri. It is formed of fourteen bones. 



1. Anterior opening, pear-shaped, Apertura pyriformis, formed by the supe- 

 rior maxillary, and nasal bones, which have attached to them the lateral nasal 

 cartilages. 



2. Posterior opening, Choanae narium, quadrangular, rather longer than 

 broad, divided by the Vomer; formed, laterally, by the Plerygoid processes,- 

 above by the Sphenoid and Palate bones ; below by the Palate bones ; looks 

 towards the Pharynx. 



3. Central division, septum narium, formed by the vertical plate of the 

 Ethmoid, by the Vomer, crista nasalis of the Frontal crista of the Nasal, Sup. 



