THE DOG’S SKULL. 29 
THE JAWS. 
The maxillary and mandibular arches arise as 
modifications of the primitive cartilaginous 
visceral arches of the embryo; thus becoming 
adapted to a function very different from their 
primitive one. In the downward growth of the 
first visceral arch, an upward and forwardly 
directed process is developed known as the 
maxillary process (palato-quadrate cartilage), 
which forms the foundation of the upper jaw of 
the adult ; growing forwards they meet with a 
cartilage, the naso-frontal process. The down- 
wardly directed portions of the arch has in the 
meantime continued its growth, and become 
united by its distal end with the process of the 
opposite side, the two forming the future lower 
jaw (Meckel’s cartilage). 
a. The maxillary arch. The bones of the 
maxillary arch enter into very close relation- 
ship with those of the olfactory capsule, and 
the ethmoidal region of the cranium. 
i. The pterygords are two plate-like bones 
lying upon the basi-sphenoid and 
ali-sphenoid. Their lateral borders are 
partly supported by the ali-sphenoids 
and palatines. Anteriorly they join 
with the posterior portions of the 
palatines. The posterior portion of 
