377 



fissure, which widens at both ends, divides the tympanic from the clamping process of the 

 squamosal : this articulates behind by a suture with the mastoid. The parietals are broad, 

 but short, and pinched in, as it were, by the temporal fossae, which almost meet at the line 

 of the sagittal suture, which is obliterated. The frontals are more than double the size of the 

 parietals, and are greatly swollen by the enormous sinuses. The most remarkable feature of 

 the Porcupine's cranium is the magnitude of the nasal bones, especially their great posterior 

 expanse, which terminates behind on the same vertical parallel as the middle of the zygomatic 

 arch. The thick anterior pier by which this inverted arch is suspended is formed by the 

 maxillary and lacrymal. The slender horizontal process of the maxillary, which bounds the 

 lower part of the antorbital vacuity, appears like a second zygoma. The premaxillaries pro- 

 gressively contract as they pass backwards and join the frontals, nearly an inch in advance of 

 the hinder border of the nasals. The bony palate terminates by a thick rounded border 

 between the last molar teeth (m 3). The pterygoids send backwards and upwards a hamular 

 process, which joins the auditory bulk : the sides of the basioccipital present a rough tract, 

 or process, which also articulates with the bulla. The last true molars (m 3) have recently 

 come into place in both jaws. The first of the series is the deciduous molar, worn down to 

 its diverging fangs, the grinding surface presenting a few small islands of enamel. In the 

 lower jaw a strong ridge extends from the outer side of the molar alveoli to the angle of the 

 jaw, which is not much produced. 



Hu uteri an. 



The following are parts of the same skeleton : 



2077. The atlas. 



The transverse process is perforated horizontally and vertically by the vertebral artery, 

 which afterwards pierces the neural arch : this is deeply grooved behind. There is a hyp- 

 apophysial tubercle. 



2078. The dentata. 



Its body is carinate below. Its spine is large, compressed, and much produced backwards. 



2079. The four succeeding cervical vertebrae. 



The pleurapophysial parts of the transverse processes are developed forwards and back- 

 wards, and overlap each other. 



2080. The last cervical vertebra. 



The pleurapophysis is simple ; but being anchylosed, as in the other cervicals, with the 

 centrum and diapophysis, forms a " perforated thin transverse process." 



2081. The dorsal vertebrae. 



They are 15 in number, as in the skeleton, No. 2075. The natural cartilages are retained, 



3 c 



