THE ZYGOMATIC BONES. 



153 



Ossification. The palate bone ossifies in membrane at the side of the nasal segment 

 of the bucco-nasal cavity, medial to the descending palatine nerves, at a time when each 

 half of the developing palatine shelf is hanging down by the side of the tongue. When 

 the palatine shelf becomes horizontal, as it does in the fifth week, bone extends into it 

 to form the horizontal plate. From this common centre all parts of the palate bone 

 develop but the orbital process may be ossified from an independent centre, which either 

 fuses with the palate bone, or with the sphenoid, or with the ethmoid. 



Ossa Zygomatica. 



The zygomatic bone (O.T. malar) underlies the most prominent part of 

 the cheek, and is hence often called the cheek-bone. Placed to the lateral side 

 of the orbital cavity, it forms the sharp lateral border of that hollow, and serves 

 to separate that space from the temporal and infra- temporal fossae which lie behind ; 

 below, it rests upon and is united to the maxilla; behind, it enters into the for- 

 mation of the zygomatic arch, which bridges across the temporal fossa. 



As viewed from the lateral side, the bone is convex from side to side, and has 

 four processes, of which three are prominent. These are the fronto r sphenoidal 



Fronto-sphenoidal process 



Fronto-sphenoidal process 



Temporal border 



Zygomatico- 

 orbital foramen 



Masseteric 

 border 



Maxillary 

 border 



Zygomatico- 

 facial canal 



For articulation 

 with maxilla 



Orbital process 



Temporal 

 process 



Infra- 

 temporal 

 surface 



A B 



FIG. 162. THE RIGHT ZYGOMATIC BONE. A, Lateral Side; B, Medial Side. 



(processus frontosphenoidalis), the marginal or pointed extremity of the maxillary 

 border, and the temporal (processus temporalis). The -most elevated part of the 

 convex malar surface (facies malaris) forms the malar tuberosity. 



The temporal process ends posteriorly in an oblique edge, which articulates 

 with the extremity of the zygomatic process of the temporal bone. The fronto- 

 sphenoidal process, the most prominent of the three, is united superiorly to 

 the zygomatic process of the frontal bone. The edge between the frontal and 

 temporal processes is thin and sharp"; it affords attachment to the temporal fascia, 

 and near its upper end there is usually a pronounced angle (processus marginalis), 

 formed by a sudden change in the direction of the border of the bone. It is just 

 below this point that the zygomatico-temporal branch of the zygomatic nerve 

 becomes cutaneous. The inferior margin of the temporal process is somewhat 

 thicker and rounded ; it extends downwards and forwards towards the inferior 

 angle, where the bone articulates with the maxilla, and is there confluent with the 

 ridge which separates the facial from the infra -temporal aspect of the maxilla. 

 This edge of the bone is sometimes called the masseteric border, since it affords 

 attachment to the fibres of origin of the masseter muscle. Sweeping downwards, in 

 front of the fronto-sphenoidal process, is a curved edge which terminates inferiorly 

 in a pointed process. This border forms the lateral and, in part, the inferior margin 

 of the orbital cavity. Between the anterior extremity of the masseteric edge and 

 the pointed anterior angle there is an irregular suture by which the bone is 

 joined to the maxilla. The opening of the foramen zygomaticofaciale (zygomatico- 



