THE SUPERIOR MAXILLA. 199 



the end of the suture behind the parietal foramina being nearly straight. The pos- 

 terior border interlocks with the squamous portion of the occipital by a very irregular 

 line of suture. The i?iferior border, concave in the middle, is bevelled on its outer 

 surface, except behind. It is covered anteriorly by the top of the great wing of the 

 sphenoid, and along the concavity by the squamous part of the temporal. The pos- 

 terior portion presents a point at the back of the concavity which fits into an angle 

 between the squamous and mastoid parts of the temporal. Behind this it is thick 

 and jagged for the top of the mastoid portion. The anterior superior corner is about 

 a right angle. The inferior one is somewhat drawn out. The superior posterior 

 corner is rounded. The inferior is cut off. 



Parietal impressions is the term applied to depressions which are observed 

 very exceptionally on the outer surface of the parietal bones above the parietal emi- 

 nences and near the upper border. They are usually large, — i.e., some seven centi- 

 metres long by five or six centimetres broad. Some sections have shown that they 

 involve only the outer surface of the bone. A thinning above the sagittal suture 

 has also been observed, and even one over the lambdoidal suture. These latter are 

 generally considered atrophic changes occurring in old age. The same explanation 

 is offered for the parietal impressions proper, and very possibly with justice ; still, the 

 case is reported by Shepherd ^ of an old woman who remembered having them all 

 her life, and who declared that her father had them likewise. This would point to 

 their being occasionally both congenital and hereditary. The late Professor Sir 

 George Humphry " observed them in the orang-outang. 



Articulations, — Each parietal articulates with its mate, the occipital, temporal, 

 sphenoid, and frontal bones. 



Development. — A single centre appears in the membrane at the end of the 

 second foetal month. According to Toldt {Lotos, 1882), this is double, consisting 

 of an upper and a lower part, which soon fuse. The centre becomes very prominent, 

 and bone-rays extend from it, making the bone very rough till after birth. The 

 fontanelles at the four corners of the bone are discussed in describing the skull as 

 a whole (page 231). The radiating lines of bone leave an interval near the back of 

 the upper border of the bone, called the sagittal fontayielle, which closes during the 

 latter part of foetal life. According to Broca, this can be seen at birth once in four 

 times. The parietal foramen is left as this fissure closes. Its occasional great size 

 is accounted for by irregularities in the process. Very rarely a suture divides the 

 parietal into an upper and a lower portion. 



THE FACE. 



The face consists of the orbits, the nose, and the jaws. Portions of the sphe- 

 noid and the ethmoid form a considerable part of it, as has been described. The 

 facial bones are two superior maxillce, two malar, two nasal, two lachrymal, two 

 palate, two inferior turbinates, the vo?ner, the inferior maxilla, and the hyoid. 

 The future nasal septum, extending in the median plane from the base of the skull 

 to the upper jaw, is very early developed in cartilage. Ossification progresses from 

 superficial centres on either side. These form the vertical plate of the ethmoid and 

 the vomer ; but a considerable part, the triangular cartilage, remains cartilaginous. 



THE SUPERIOR MAXILLA. 



The superior maxilla '^ is a very irregular bone, which with its fellow forms the 

 front of the upper part of the face, the floor of the orbit, much of the outer wall and 

 floor of the nasal cavity, much of the hard palate, and supports all the upper teeth. 

 It has a body, and malar, nasal, alveolar, and palatal processes. The general shape 

 of the body * is that of a four-sided pyramid ; the base looking towards the nasal 

 cavity, one surface forming the floor of the orbit and the other two the front and 

 back of the bone. These three surfaces meet at the apex, which is the vialar process.^ 



^Journal of Anatomy and Physiology, vol. xxvii., 1893. 

 ^ Ibid, vol. viii., 1874. 



' Maxilla. ''Corpus maxillae. ^ Processus zygomaticus. 



