LACHRYMAL BONES. 



163 



1 far Ifa *cul 



i for Orbital, 

 Malar 



Anterior Surface. 



at 

 Birth 



I for Palata 



"erior Surface. 



corresponding ridge in the opposite bone, forms a groove for the reception of 



the voraer. The anterior margin is bounded by the thin concave border of the 



opening of the nose, prolonged 



forwards internally into a sharp Fig. 114 Development of Superior Maxillary Bone. 



process, forming, with a similar B ? four Centre8 ' 



process of the opposite bone, 



the anterior nasal spine. The 



posterior border is serrated for 



articulation with the horizontal 



plate of the palate bone. 



Development. This bone is 

 formed at such an early peripd, 

 and ossification proceeds in it 

 with such rapidity, that it has 

 been found impracticable hi- 

 therto to determine with ac- 

 curacy its number of centres. 

 It appears, however, probable 

 that it has four centres of de- 

 velopment, viz., one for the 

 nasal and facial portions, one 

 for the orbital and malar, one 

 for the incisive, and one for the 

 palatal portion, including the 

 entire palate, except the incisive 

 segment. The incisive portion 

 is indicated in young bones by 



a fissure, which marks off a small segment of the palate, including the two 

 incisor teeth. In some animals, this remains permanently as a separate piece, 

 constituting the intermaxillary bone ; .and in the human subject, where the jaw 

 is malformed, as in cleft palate, this segment may be separated from the maxil- 

 lary 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 : they are not unfre- 

 quently much displaced, and the deformity is often accompanied by congenital 

 fissure of the 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 nasal sinuses, 

 its development commencing about the fourth month of foetal life. 



Articulations. With nine bones ; two of the cranium the frontal and eth- 

 moid, and seven of the face, viz., the nasal, malar, lachrymal, inferior turbi- 

 nated, palate, vomer, and its fellow of the opposite side. Sometimes it articu- 

 lates with the orbital plate of the sphenoid. 



Attachment of Muscles. Orbicularis Palpebrarum, Obliquus Inferior Oculi, 

 Levator Labii Superioris Alaeque Nasi, Levator Labii Superioris Proprius, 

 Levator Anguli Oris, Compressor Nasi, Depressor Alae Nasi, Masseter, 

 Buccinator. 



THE LACHRYMAL BONES. 



The Lachrymal are the smallest and most fragile bones of the face. They 

 are 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 the 

 ossa unguis. Each bone presents, for examination, two surfaces and four 

 borders. The external (Fig. 115) or orbital surface 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 



