THE LACHRYMAL BONES. 195 



superior maxilla. The antrum appears as a shallow groove on the inner surface 

 of the bone at an earlier period than any of the other nasal sinuses, its develop- 

 ment commencing about the fourth month of foetal life. The sockets for the 

 teeth are formed by the growing downward of two plates from the dental groove, 

 which subsequently becomes divided by partitions jutting across from the one to 

 the other. 



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, and sometimes with its external pterygoid plate. 



Attachment of Muscles. To twelve : the Orbicularis palpebrarum, Obliquus 

 oculi inferior, Levator lalm superioris alseque nasi, Levator labii superioris 

 proprius. Levator anguli oris. Compressor nasi, Depressor alse nasi. Dilatator 

 naris posterior. Masseter, Buccinator, Internal pterygoid, and Orbicularis oris. 



CHANGES PRODUCED IX THE UPPER JAW BY AGE. 



At birth and during infancy the diameter of the bone is greater in an antero-posterior 

 than in a vertical direction. Its nasal process is long, its orbital surface large, and its tuberosity 

 well marked. In the adult the vertical diameter is the greater, owing to the development of 

 the alveolar pr-nvss and the increase in size of the antrum. In old age the bone approaches 

 again in character to the infantile condition : its height is diminished, and after the loss of the 

 teeth the alveolar process is absorbed, and the lower part of the bone contracted and diminished 

 in thickn. 



The Lachrymal Bones. 



The Lachrymal (laebryma, a tear) 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 o**</ unyuis. Each bone presents for examination two surfaces and 

 four borders. The external or orbital surface (Fig. 158) is divided by a vertical 

 ridge, the lachrymal /> *f. 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 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, 

 with a part of the orbital surface immediately behind it, 

 affords attachment to the Tensor tarsi : the ridge terminates 

 below in a small, hook-like projection, the hamular process, 

 which articulares with the lachrymal tubercle of the superior 

 maxillary bone, and completes the upper orifice of the lach- 

 rymal groove. It sometimes exists as a separate piece, which rymai bone. External 

 is then called the lesser Minimal bone. The internal or nasal fS^f,' (Sli s htl y en " 

 surface presents a depressed furrow, corresponding to the 

 ridge <>n irs 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 

 nvo r-arts : the posterior part articulates with the orbital plate of the superior 

 maxillary bone : the anterior portion is prolonged downward into a pointed pro- 

 cess, which articulates with the lachrymal process of the inferior turbinated bone 

 and assists in the formation of the lachrymal groove. 



