THE SKULL AS A WHOLE 161 



There is usually a foramen in the temporo-occipital suture above the root of the 

 paramastoid process. The foramen magnum varies greatly in form; most often 

 the transverse diameter is the greater, l)ut in some skulls it is equaled or exceeded 

 by the vertical diameter. 



The cranial cavity (Fig. 124) corresponds in form and size with the cranium, 

 specially in those breeds in which the various crests are more or less effaced and the 

 frontal sinuses are small. The basi-cranial axis is almost parallel with the palate, 

 and the floor is flattened. The anterior fossa is narrow and is only slightly higher 

 than the middle one. The olfactory fossae are very deep and the crista galli is little 

 developed. The sella turcica is variable in depth, and the dorsum sellae is relatively 

 high and bears clinoid processes laterally. The cerebral and cerebellar compart- 

 ments are well marked off laterally by the petrosal crests and above liy the ten- 

 torium osseum. The base of the latter is traversed by a canal which connects 

 the two parieto-temporal canals. The anterior angle of the petrous temporal is 

 perforated by a canal for the fifth cranial nerve. 



The nasal cavity (Fig. 373) conforms to the shape of the face. Its anterior 



Fig. 127. — Skull of Br.\chyceph.\lic Dog, L.vteral View withot't Mandible. 



aperture is large and nearly circular in most dogs. The complex inferior turbinals 

 occupy the anterior part of the cavity to a large extent, except near the aperture. 

 Behind the inferior turbinals is the large opening of the maxillary sinus. Behind 

 this the cavity is divided by a horizontal plate (Lamina transversalis) into a large 

 upper olfactory region or fundus nasi and a lower naso-pharyngeal canal. The 

 fundus is occupied largely by the ethmoturbinals. The posterior nares are undi- 

 vided and are in general long and narrow, but vary with the shape of the skull. 



The frontal sinus is of considerable size in the large breeds, but is confined to 

 the frontal bone. It is usually divided into a small anterior and a much larger 

 posterior compartment, each of which opens into the superior ethmoidal meatus. 

 The sinus is very small in extreme brachycephalic types. 



The maxillary sinus is small, and is in such free communication with the 

 nasal cavity as to make it rather a recess than a true sinus. It is bounded 

 internally by the lamina papyracea of the ethmoid, and its outer wall is 

 crossed obliquely by the lacrimal canal. The roots of the molar teeth do 

 not project up into it. 

 11 



