1000 ORGANS OF THE SENSES AND THE COMMON INTEGUMENT 



orbital canal, while its floor is formed by the alveolar process and is usually \ to 10 

 mm. below the level of the floor of the nose; projecting into the floor are several 

 conical elevations corresponding with the roots of the first and second molar teeth, 

 and in some cases the floor is perforated by one or more of these roots. The size 

 of the sinus varies in different skulls, and even on the two sides of the same skull. 

 The adult capacity varies from 9.5 c.c. to 20 c.c., average about 14.75 c.c. The fol- 

 lowing measurements are those of an average-sized sinus: vertical height opposite 

 the first molar tooth, 3.75 cm.; transverse breadth, 2.5 cm.; antero-posterior depth, 

 3 cm. In the antero-superior part of its base is an opening through which it com- 

 municates with the lower part of the hiatus semilunaris ; a second orifice is frequently 

 seen in, or immediately behind, the hiatus. The maxillary sinus appears as a shal- 

 low groove on the medial surface of the bone about the fourth month of fetal life, 

 but does not reach its full size until after the second dentition. 1 At birth it measures 

 about 7 mm. in the dorso-ventral direction and at twenty months about 20 mm. 2 



Frontal sinus 



Frontal ostium 

 Infundibulum cells 



Fossa of lacrimul sac 



Maxillary ostium 

 Maxillary septum - 



Ant. ethmoidal air cells 



Post, ethmoidal air cells 

 ic nerve 



FIG. 862. Specimen from a child eight years, eight months, and one day old. Lateral view of frontal, ethmoidal and 

 maxillary sinus areas, the lateral portion of each having been removed by sagittal cuts. Note that the sinusfrontalis 

 developed directly from the infundibulum ethmoidale. Note also the incomplete septa in the sinus maxillaris. (Davis.) 



THE ORGAN OF SIGHT (ORGANON VISUS; THE EYE). 



The bulb of the eye (bulbus oculi; eyeball), or organ of sight, is contained in the 

 cavity of the orbit, where it is protected from injury and moved by the ocular 

 muscles. Associated with it are certain accessory structures, viz., the muscles, 

 fasciae, eyebrows, eyelids, conjunctiva, and lacrimal apparatus. 



The bulb of the eye is imbedded in the fat of the orbit, but is separated from it 

 by a thin membranous sac, the fascia bulbi (page 1024) . It is composed of segments 

 of two spheres of different sizes. The anterior segment is one of a small sphere; 



1 The various measurements of the accessory sinuses of the nose are baaed on those given by Aldren Turner in hi* 

 Accessory Sinuses of the Nose. 



2 Schaeffer, J. P., Am. Jour. Anat., 1910, x. 



