86 OSTEOLOGY. 



in the human subject, where the jaw is malformed, as in cleft palate, this segment 

 may be separated from the maxillary bone by a deep fissure extending backwards 

 between the two into the palate. If the fissure be on both sides, both segments are 

 quite isolated from the maxillary bones, and hang from the end of the vomer, not 

 unfrequently being much displaced, and often accompanied by congenital fissure of 

 die upper lip, either on one or both sides of the median line. The maxillary sinus 

 appears at an earlier period than any of the other sinuses, its development com- 

 mencing about the fourth month of foetal life. 



Articulations. With nine bones : two of the cranium the frontal and ethmoid, 

 and seven of the face, viz., the nasal, malar, lachrymal, inferior turbinated, palate, 

 vomer, and its fellow of the opposite side. Sometimes it articulates with the 

 orbital plate of the sphenoid. 



Attachment of Muscles. Orbicularis palpebrarum, Obliquus inferior oculi, Leva- 

 tor labii superioris alaeque nasi, Levator labii superior] s proprius, Levator anguli 

 oris, Compressor naris, Depressor alas nasi, Masseter, Buccinator. , 



THE LACHEYMAL BONES. 



The Lachrymal Bones are the smallest and most fragile bones of the face, situated 



at the front part of the inner wall of the orbit, and resemble somewhat in form, 



thinness, and size, a finger-nail ; hence they are termed 



Fig. 48. Left Lachrymal the ossa unguis. Each bone presents for examination two 

 Bone. External Surface. sur f ace s and four borders. The external or orbital surface 

 vi -a Frontal ( n g- 48) is divided by a vertical ridge into two parts. The 



portion of bone in front of this ridge presents a smooth,- 

 concave, longitudinal groove, the free margin of which 

 unites with the nasal process of the superior maxillary bone, 

 completing the lachrymal groove. The upper part of this 

 groove lodges the lachrymal sac ; the lower part assists in 

 the formation of the lachrymal canal, and lodges the nasal 

 duct. The portion of bone behind the ridge is smooth, 

 slightly concave, and forms part of the inner wall of the 

 orbit. The ridge, and part of the orbital surface imme- 

 diately behind it, afford attachment to the Tensor tarsi : 

 (Stir/My tnla-rycd \ the ridge terminates below in a small hook-like process, 

 which articulates with the lachrymal tubercle of the supe- 

 rior maxillary bone, and completes the upper orifice of 



the lachrymal canal. It sometimes exists as a separate piece, which is then 

 called the lesser lachrymal lone. The internal or nasal surface presents a depressed 

 furrow, corresponding to the ridge on its outer surface. The surface of bone in 

 front of this forms part of the middle meatus ; and that behind it articulates 

 with the ethmoid bone, filling in the anterior ethmoidal cells. Of the four borders, 

 the anterior is the longest, and articulates with the nasal process of the superior 

 maxillary bone. The posterior, thin and uneven, articulates with the os planum 

 of the ethmoid. The superior, the shortest and thickest, articulates with the 

 internal angular process of the frontal bone. The inferior is divided by the lower 

 edge of the vertical crest into two parts, the posterior part articulating with the 

 orbital plate of the superior maxillary bone ; the anterior portion being pro- 

 longed downwards into a pointed process, which articulates with the lachrymal 

 process of the inferior turbinated bone, assisting in the formation of the lachrymal 

 canal. 



.Development. By a single centre, which makes its appearance soon after ossi- 

 fication of the vertebrae has commenced. 



Articulations. With four bones : two of the cranium, the frontal and ethmoid, 

 and two of the face, the superior maxillary and the inferior turbinated. 

 Attachment of Muscles. The Tensor tarsi. 



X 



