164 
ME. GEORGE W. CALLENDER ON THE FORMATION AND 
membrane, which extends from the lower edge of the internasal plate, with the peri- 
chondrium of which it is continuous, to the inner side of either lateral mass over which 
it is prolonged. By such membrane the passage of either nostril is completed, the 
anterior orifice being bounded by the cartilage of the nose above, by the extremity of 
the internasal cartilage in the middle line, and between these structures by the con- 
necting membrane. Where the latter passes off from the septum, there is an elevation 
of tissue on either side of a central depression. 
In a human foetus four-tenths of an inch long the frontal-nasal process is still distinct ; 
the lateral-nasal and the maxillary lobe, united, approach it on either side, most nearly 
above, and the maxillary lobe can be traced back as a slight elevation, the palate, 
towards the middle line (Plate XIII. fig. 1). On raising the frontal-nasal process the 
central part of its under surface is found to form two thickened masses, and represents 
the nasal cartilages, and from either side of this central part a narrow ridge curves down- 
wards, the cartilage for the future ethmoid and turbinate bones (Plate XIII. fig. 2). 
These central parts growing forward are joined, beginning from above, to the maxillary 
lobes in a foetus nine-tenths of an inch long, the union of opposite sides to form the 
palate taking place gradually from before backwards. In a foetus P5 the union of the 
maxillary lobes is not yet complete, a fissure still extending through the soft palate. 
If in a foetus nine-tenths of an inch long the superficial parts are removed, that 
portion which forms the superior maxilla is seen to occupy the position, and to have 
the shape of the future bone, the orbital, palatal, and alveolar parts being defined, whilst 
two considerable projections indicate the position of the nasal and of the incisor pro- 
cesses, the last named lying immediately above the elevation, or thickening, at the 
anterior extremity of the internasal cartilage. The mass of the superior maxilla consists 
of cells crowded together, having well-defined outlines, and being filled with granular 
matter. After the development of the. bone its subsequent growth is effected in the 
membrane which covers its various surfaces, and in the membranous part of the nasal 
wall. 
Ossification and Growth of the Superior Maxilla. 
No ossification has taken place in the superior maxilla of a foetus nine-tenths of an 
inch long, but in a foetus IT numerous bony deposits are visible. These independent 
bone formations appear in that portion of the maxillary lobe which has been described 
as moulded to the shape of the upper jaw. The most conspicuous are ranged below 
the infraorbital plate, and stud the alveolar border and the nasal process ; but although 
ossification commences at many distinct points in these parts of the bone, the rapidity 
with which the separate ossifications are fused makes it undesirable to name each as a 
distinct centre. In a foetal pig 2 inches long (Plate XIII. fig. 3) the superior maxilla, 
besides a well-formed palatal portion, consists of osseous deposits which seem to radiate 
from a line corresponding with the base of the alveoli, and from a centre situated imme- 
diately below the infraorbital notch. A somewhat similar condition is observable in the 
mammary foetus, nine-tenths of an inch long, of a Kangaroo. 
