SKULL OF A HUMAN FETUS OF 40 MM. ' 323 



wards, except where cut off by the zygomatic bone and the 

 maxilla, and but imperfectly closed behind. In the posterior 

 portion of the orbit is seen the elongated optic foramen, and the 

 closeness of apposition of the sphenoidal and ectethmoidal 

 cartilages is to be observed. An open space, communicating 

 freely above with the orbit, below with the cavity of the mouth 

 and medially with that of the pharynx, is seen in front of the ala 

 temporalis, the medial wall of the space being indicated by the 

 imperfectly developed vertical plate of the palatine bone and by 

 the rudimentary medial pterygoid plate. The position of the 

 as yet unformed pterygomaxillary fossa is indicated in this space 

 by the sphenopalatine ganglion (fig. 14) (not shown in the model), 

 and lateral to this, bounded by the incomplete zygomatic arch, 

 are the temporal and zygomatic fossae. One is struck with the 

 lack of prominence of the zygomatic region when compared with 

 the osseous skull, the zygomatic bone and arch being completely 

 overhung by the lateral part of the cranial floor. That this 

 disproportion is partly due to the shallowness of the temporal 

 and zygomatic fossae is evident from a comparison of the model 

 with the bony skull. It would appear that the lateral growth 

 of the ala temporalis of the sphenoid and of the zygomatic 

 process of the maxilla, combined with thickening of the tempor- 

 alis muscle, are the principal factors which bring about the widen- 

 ing of the temporal and zygomatic fossae, and consequent out- 

 pushing of the lateral parts of this area. It is evident from a 

 comparison of the skulls of the newborn and the adult that this 

 change continues till some time after birth. 



The lower part of the facial region is characterized by the 

 gaping cavity of the moUth, bounded above by the superior 

 maxilla and below by Meckel's cartilage with its covering bone, 

 the mandible (fig. 4). The lack of prominence of the angle of 

 the latter, due to the shortness and inclination of the ramus and 

 its relative nearness to the medial sagittal plane, may be ob- 

 served, and it will also be seen that there is a small space between 

 the articular process of the mandible and the position of the future 

 glenoid cavity of the squamo-temporalis (fig. 4). The coronoid 

 process of the mandible is quite close to the ala temporalis of the 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 16, NO. 3 



