88 THE SKELETON. 



and the malar process ; 3. A third from which is developed the palatine process 

 posterior to Stenson's canal and the adjoining part of the nasal wall; 4. And 

 a fourth for the front part of the alveolus which carries the incisor teeth 

 and corresponds to the pre-maxillary bone of the lower animals. These 

 centres appear about the eighth week, and by the tenth week the three first- 

 named centres have become fused together and the bone consists of two por- 

 tions, one the maxilla proper, and the other the pre-maxillary portion. The 

 suture between these two portions on the palate persists till middle life, but 

 is not to be seen on the facial surface. This is believed by Callender to be 

 due to the fact that the front wall of the sockets of the incisive teeth is not 

 formed by the pre-rnaxillary bone, but by an outgrowth from the facial part of the 

 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 labii superioris alaeque nasi, Levator labii superioris 

 proprius, Levator anguli oris, Compressor nasi, Depressor alae nasi, Dilatator 

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



CHANGES PRODUCED IN 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 process and the increase in size of the antrum. In o-ld 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 thickness. 



The Lachrymal Bones. 



The Lachrymal (lachryma, 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 (Fig. 

 46). 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 or orbital surface (Fig. 53) is divided by a vertical 

 ridge, the lachrymal crest, 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, 

 aifords attachment to the Tensor tarsi muscle : it terminates 

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

 r which articulates with the lachrymal tubercle of the superior 



FIG. 68.-Left lach- maxillar j ^one, and completes the upper orifice of the lach- 

 su?face bon (siight]iy er en- !7 mal g roove - Jt sometimes exists as a separate piece, which 

 larged.) is then called the lesser lachrymal bone. 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 



