SKELETON OF RODENTIA. 



373 



is short, directed outward and a little forward, and is notched 

 behind. A fissure, which Avidens at both ends, di^ddes the tym 

 panic from the clamping process of the squamosal : this articulates 

 behind by a suture with the mastoid. The parietals, fig. 239, 7, are 

 broad, but short, and pinched in, as it were, by the temi)oral fossix?, 

 w hich almost meet at the line of the sagittal suture, which is obli- 

 terated. The frontals, ib. ii, are more than double the size of the 

 parietals, and are greatly swollen by the enormous sinuses. Tlie 

 most remarkable feature of the Porcupine's cranium is the magni- 

 tude of the nasal bones, 15, especially their great posterior expanse, 

 which terminates behind on the same vertical parallel as the middle 

 of the zygomatic arch. This character is contrasted in iig. 239 

 with the small size of the nasals, 15, in the Manatee and Capuchin 

 Monkey. The thick anterior pier by which the zygomatic arch is 

 suspended is formed by the maxillary and lacrymal. The slender 



Porcupine. 



horizontal process of the maxillary, which bounds the lower part 

 of the antorbital vacuity, fig. 238, v, appears like a second zygoma. 

 The premaxillaries progressively contract as they pass backward 

 and join the frontals, nearly an inch in advance of the hinder bor- 

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

 border between the last molar teeth. The pterygoids send back- 

 ward and upward a hamular process, which joins the tympanic 

 bulla. The cerebellar depression upon the petrosal is very shallow : 

 the fore part of the petrosal presents a large protuberance. The 

 rhinencephalic fossa is relatively of large size, and is defined by a 

 well-marked ridge from the rest of the cranial cavity. Two vascu- 

 lar canals are continued into its lower part from above the optic 

 foramina, instead of an open groove, as in the Agouti. The 

 coalesced prefrontals are compressed. The vomer is deeply cleft 

 posteriorly, and has coalesced mth the ethmoturbinals, and its 

 anterior part articulates with the median ascending process of the 

 premaxillary arching over the wide vacuities which lead from the 

 nasal passages to the prepalatine apertures, as in most Rodents. 



