10 OSTEOLOGY OP SCOMBUOID PISHES 



of the supraoccipitul crest. These and the median supraoccipital ridge 

 are finely sculptured on their upper edges, and in the undissected speci- 

 men are externally visible, being covered only with very thin skin. Be- 

 tween the frontal ridges there is a broad median area depressed below 

 the level of the supraorbital region on the outer side of the frontal 

 ridges. From the sphenotic a sharp ridge curves upward to the poste- 

 rior end of the great frontal ridge, joining it near its union with the 

 lateral ridge of the supraoccipital crest. In the base of the lower end 

 of this ridge is the opening of a sensory tunnel, which curving upward 

 and backward pierces the great frontal ridge, and opens at the poste- 

 rior end of the frontal near the supraoccipital. This sensory tunnel is 

 in continuation with the suborbital and pterotic tunnels, and also with 

 the frontal tunnel, which runs forward traversing longitudinally the 

 great frontal ridge and thence the nasal. 



The supraoccipital extends back in a high triangular crest without 

 either extending forward over the frontals, or being in continuation 

 with a median frontal ridge. Following its entire upper contour on 

 each side is a lateral ridge, which is in continuation with the high ridge 

 on each frontal as described above. Posteriorly the supraoccipital ex- 

 tends down over the exoccipital suture, but it does not reach to the fora- 

 men magnum. 



The exoccipitals meet both above and below the foramen magnum, 

 and their vertebral articular fascets are nearly in contact above the 

 basioccipital. Each bears three foramina more or less in a horizontal 

 line. The middle one, the vagus foramen, has two smaller foramina close 

 beside it, and the anterior one, the glossopharyngus foramen, is only par- 

 tially contained by the exoccipital, being between that bone and the 

 prootic. The posterior one, the foramen of the occipital nerve, is situ- 

 ated on the ridge that runs forward from the exoccipital condyle to the 

 pterotic crest. 



The whole lower posterior part of the basioccipital is occupied by a 

 very large opening to the myodome, filling the width of the bone and 

 leaving its side walls thin. From the upper posterior edge of the basi- 

 occipital is a sharp ridge running downward and forward to its lower 

 edge just in front of the posterior opening to the myodome. Between 

 this and the basioccipital condyle are some pits ending blindly, but re- 

 sembling neural foramina. 



The parasphenoid bears a thin median keel below, behind which is 

 a saddle-shaped notch where on each side the first toothless pharyngeal 

 lies. Just back of this is a swollen knob for the support of the other su- 

 perior pharyngeals, and still farther back, extending under the knob, 



