THE SKULL THE CEANIUM 275 



and medially across the lamina to the opening of the Vidian canal 

 corresponds to the long Vidian groove on the inferior surface of the 

 sphenoid of the cat. Lateral to this groove a wider depression leads 

 to the scaphoid fossa and lodges part of the Eustachian tube. The 

 outer end of the spheno-petrosal lamina projects dorsally and laterally 

 and corresponds to the real posterior angle of the cat's alisphenoid, 

 while the human sphenoidal angle, which is lateral to the foramen 

 spinosum and is often produced ventrally in an angular spine, cor- 

 responds to the roughened elevation in the cat's alisphenoid which 

 lies just behind the foramen ovale and marks the anterior attachment 

 of the ectotympanic. The posterior margin of the great wing joins 

 the petrous of the temporal only by its outer parts, leaving between 

 its inner part, the petrous, and the basisphenoid a vacuity filled in the 

 recent state by a plate of cartilage which is pierced by the carotid 

 artery. This opening is the middle lacerated foramen, so called to 

 distinguish it from the sphenoidal fissure, sometimes termed the anterior 

 lacerated foramen, and from the jugular foramen, sometimes termed the 

 posterior lacerated foramen. It is rudimentary in the cat, and limited 

 to a small opening between the notch medial to the lingula and the 

 dorsal of the two anterior projections of the ectotympanic. The 

 human angular spine is often marked on the medial side by a groove 

 for the chorda tympani nerve. 



THE FRONTAL BONES. 



General Description. The paired unsymmetrical frontal bones 

 form the anterior end of the cranium (Fig. 198). They limit the 

 cranial cavity in front as the occipital limits it behind, and present 

 between them an oblong foramen which would lead into the cavities 

 in the face were it not closed by the cribriform plate of the ethmoid 

 (Figs. 199, 200). The frontals form the greater part of the inner and 

 upper walls of the orbits, wherein are lodged the eyes, a large part 

 of the upper and outer walls of the nasal cavities, and a small part of 

 the temporal fossae (Fig. 200). In old skulls the two frontals are 

 sometimes united, and the interfrontal part of the sagittal suture 

 known as the metopic suture may be entirely obliterated ; in skulls 

 of ordinary age, however, the two bones can be easily separated. 



Each frontal consists of two well-marked parts : a smooth, slightly 

 convex, horizontal plate, covered by the scalp and forming the fore- 



