253 



fossa (Plate XXXVII. figs. 2 & 3, t). The parietal or parieto-temporal wall (Plate 

 XXXVI. fig. 1, 7 ) is divided from the occipital plane (Plate XXXVII. fig ; 2, 3 ) by the 

 superior or superoccipital arched ridge ; it is divided from its fellow or opposite wall 

 above by a flattened tract about an inch broad (ib. fig. 2, 7), near the superoccipital (ib. 

 fig. 2, 3), but which expands as it advances from the parietal (7) upon the frontal (11) region. 

 The parieto-frontal part of the cranium forms less than the middle third of the breadth 

 of the entire skull as here completed by the enormous zygomatic arches. The frontal 

 roof of the cranium, retaining its flatness transversely, gains a breadth of five inches, 

 with a slight downward slope in profile (Plate XXXVI. fig. 1), and then (ib. n) more 

 abruptly arches down to the origin of the nasals (ib. 15), an arch being continued outward, 

 on each side of the naso-maxillary pedicle, to the tuberosity (s) representing the antor- 

 bital or lacrymal process. There is a transverse depression above the origin of the nasal 

 bone (Plate XXXVII. fig. 2, is). The vertically convex outswellings of the frontal above 

 and alongside this depression indicate the enormous air-sinuses within. The inner side 

 or walls of the orbito-temporal vacuities sink sheer from the upper parieto-frontal tract 

 to the outswelling of the maxillary molar alveoli (ib. 21), with a slight inclination inward. 

 The greatest posterior depth of this cranial precipice is 65 inches. 



At the junction of the alisphenoid with the parietal, near the bottom of the back 

 wall, is a tuberosity. The diameter of the sphenoido-parietal part of the cranium is 4^ 

 inches; that of the skull at the corresponding part across, or including the zygomatic 

 arches, is 16 inches! The cranium proper, from this singular constriction, gradually 

 expands as it advances to the superorbital part of the frontals. If the cranial cavity 

 concurred with its outer walls in shape it would be triradiate, two corridors extending 

 along the transversely extended and antero-posteriorly contracted occipital part, and a 

 third passage running forward from the mid line toward the face. But the singular 

 departure in the outer walls from the normal shape of the brain-case is mainly due to a 

 vast diploe of air-cells. The proper cerebral cavity makes no outward show, and it is 

 insignificantly small in proportion to the entire skull. 



Viewed from below (as in Plate XXXVII. fig. 3), the condyles (2, 2) are divided by a 

 deep notch ; their lower ends descend a little below the level of the basioccipital ( 1 ). This 

 presents a rugged triangular tract in advance of the foramen, the apex being continuous 

 with a sharp ridge longitudinally bisecting the surface of the basisphenoid. On each 

 side of the tuberous tract and ridge is a wide and moderately deep depression, extending 

 from the lower end of the occipital condyles forward to the pterygoid plates or posterior 

 aperture of the nares. These " basioccipito-sphenoidal depressions" are bounded laterally 

 by a small tuberosity, by the inner surfaces of the occipito-petrous prominence, and by 

 a ridge inclining mesiad to the hind part of the base of the pterygoid plate. 



The basioccipito-sphenoidal part of the " basis cranii" is 3^ inches in length, and 3 

 inches in breadth posteriorly. Its plane forms with that of the " basis faciei," or bony 

 palate, lengthwise, an angle of 130°; the basis cranii sinking, the basis faciei rising, as 

 they advance. 



