154 OSTEOLOGY. 



facial foramen) is seen on the lateral surface of the bone ; its size and position 

 are very variable. 



The medial aspect of the bone is distinguished by a curved elevated crest, called' 

 the orbital process, which extends medially and backwards, and is confluent 

 laterally with the orbital margin. This process has two surfaces one anterior, 

 which forms a part of the lateral and lower wall of the orbit, and one posterior, 

 which is directed towards the temporal fossa above and the infra- temporal fossa 

 below. The free edge of the orbital process is thin and serrated ; a little below 

 its middle it is usually interrupted by a non-articular notch, which corresponds 

 to the anterior extremity of the inferior orbital fissure. The part above this 

 articulates with the great wing of the sphenoid, the portion below with the orbital 

 surface of the maxilla. Behind the orbital process the medial surface of the bone is 

 concave from side to side, and extends backwards along the medial aspect of the 

 temporal process and upwards over the posterior half of the medial side of the 

 frontal process, thus entering into the formation of the infra- temporal and temporal 

 fossae respectively. The orbital surface of the orbital process usually displays the 

 openings of two canals (foramina zygomatico - orbitalia) one which traverses the 

 bone below the orbital margin and appears on the front of the bone as already 

 described, .the other which passes obliquely upwards and laterally through the 

 orbital process and appears in the temporal fossa, to the medial side of the frontal 



process (foramen zygomaticotemporale). The former 

 transmits the zygomatico-facial branch, the latter the 

 zygomatico- temporal branch of the zygoma tic nerve. 

 Just under the orbital margin and a short distance- 

 below the zygoma tico-frontal sutures there is usually 



^^=^^^*^-^= a * a gmall tubercle serving for the attachment of the 

 lateral palpebral raphe. (Whitnall, Journ. Anat. 



Club-shaped process ^ PhyM., Vol. xlv.) 



B * low ^e orbital process there is a rough tri- 

 angular area, bounded laterally by the maxillary 

 border. This articulates with the zygomatic process of the maxilla, and occasionally 

 forms the lateral wall of the maxillary sinus. 



Connexions. The zygomatic bone articulates with the frontal, sphenoid, maxilla, and 

 temporal bones. 



Ossification. The zygomatic ossifies in membrane. Its basis appears about the tenth 

 week as a thin ossifying lamina which corresponds to the orbital margin, attached to 

 which there is a backward expansion corresponding to the body of the bone ; from this 

 posteriorly there extends the element of the temporal process. On the medial side, and 

 lying within the angle formed by the orbital and temporal elenients, there appears a 

 secondary thickening, which develops into a cup -shaped layer which fits into the recess 

 and ultimately forms the surface of the bone directed to the temporal fossa. Below 

 the orbital margin on the medial side, and extending backwards towards the temporal 

 process, is another secondary thickening, which forms a club-shaped nodule, the thick 

 end of which is directed forwards, whilst posteriorly it forms, in part, the lower margin 

 of the body and temporal process. The overlap of these several parts leads to the 

 formation of grooves which may persist in the adult as sutures. (Karl Toldt, junr., 

 Sitzsbr. des Akad. des Wiss., Wien, July 1902.) Regarding the ossification of this bone 

 there are great differences of opinion ; not a few anatomists describe it as developed from 

 a single centre. Support, however, is given to its origin from multiple centres owing to 

 the frequency with which in the adult it is met with in a divided condition. 



lYlandibuIa. 



The mandible or lower jaw, of horse-shoe shape, with the extremities up- 

 turned, is the only movable bone of the face. Stout and strong, it supports 

 the teeth of the lower dental arch, and articulates with the base of the cranium, 

 by the joints, on either side, between its condyles and the mandibular fossse of the 



