202 BONES OF THE FACE. 



opening, says Mr. Nasmyth, "presents much variety, both. 

 in direction and position, sometimes looking obliquely for- 

 wards, at others obliquely backwards, and being sometimes 

 in the anterior and sometimes in the posterior portion of 

 the nasal process." It is stated to be about the diameter of 

 a crow quill, and when deprived of the soft parts, to measure 

 from thirty to forty lines in circumference. The mucous 

 membrane also diminishes the opening. The antrum has 

 its cavity sometimes divided by septa into cells. Its roof has 

 the infra-orbital canal running along it, and terminating 

 in the infra-orbital foramen. This roof is very thin, and 

 readily allows tumors of the antrum to project into the 

 orbit. The floor has but a thin partition between the roots 

 of the teeth and this cavity, so thin indeed in some cases, 

 that the apices of the molar teeth are seen to project into 

 the sinus, and hence this is here regarded as the most eli- 

 gible spot for puncturing the antrum, and drawing off any 

 purulent collections it may contain. By some, the alveolus 

 of the canine tooth is thought most convenient for entering 

 the maxillary sinus. 



The anterior and posterior walls of this sinus contain 

 the anterior and posterior dental canals, for transmitting 

 the dental nerves and vessels. The opening of the antrum 

 communicates, by one or two small oblique orifices, with 

 the middle meatus of the nose, and anterior to it is the 

 funnel-shape tube, the infundibulum, connecting with the 

 frontal sinus and anterior ethmoid cells. 



The foramina in each superior maxillary bone are six in 

 number 2 proper and 4 common. The proper are the 

 infra-orbital and foramen incisivum. The common are the 

 foramen of the antrum, the posterior palatine, the anterior 

 nares, the opening into the nasal or lachrymal duct, and 

 the splieno-maxillary fissure. 



The number of processes is eight, viz: the orbital, nasal, 

 the tuberosity, the alveolar, malar, palatine, the nasal 

 spine, and the nasal crest. 



The structure of the upper maxillary is thick and cellu- 

 lar in its processes, and very thin, but compact about the 



