EELIS SPELiEA. 47 



The petrosal proper is so irregular in shape as almost to defy description. It may, 

 however, be conceived as resembling a dried distorted pear, lying diagonally across the axis 

 of the skull, so that the pointed end or stem points forwards, inwards, and somewhat 

 downwards. It has three well-marked sides or divisions, the intero-posterior or cerebellar, 

 the superior or tentorial, and the extero- anterior or tympanic. There is also a smooth, 

 rounded, triangular surface between the posterior edges of the tympanic and cerebellar 

 surfaces, which is partly in contact with the paroccipital (paramastoid), and partly forms 

 the inner surface of the " foramen lacerum posterius." The names of these surfaces 

 adequately show the position of the bone in the skull, for it is wedged in between the 

 basi-occipital, the tentorium, and the tympanic, the inner surface alone being exposed on 

 the side Avail of the cerebellar cavity. The inferior edge between the cerebellar and 

 tympanic surfaces is in contact with the exterior edge of the basi-occipital, the outer 

 portion of the tentorial with the lower or inner edge of the squamosal, and the anterior 

 apex of the stem reaches as far forwards as the extero-posterior angle of the basi- 

 sphenoid. The cerebellar surface of the petrosal proper is roughly eUiptical in form, 

 having the anterior end pointed. A low ridge, running diagonally upwards and forwards, 

 divides it into two long, shallow depressions. Near the middle of the lower depression is 

 the " meatus auditorius internus," a foramen somewhat C-shaped externally, but divided 

 internally into two canals, the one for carrying the facial-motor nerve, the other for the 

 body of the acoustic nerve before its distribution in the cochlea and semi-circular canals. 

 In the middle of the upper depression is the small foramen of the "aquseductus vestibuli," 

 as in man. That of the aquseductus cochlege is under the meatus auditorius, opening 

 into the petrosal sinus, rather further back than in man. The antero-inferior edge of this 

 surface is, as we have said, in contact with the basi-occipital. Between the two is the 

 " infra-petrosal sinus," which ends posteriorly in the "foramen lacerum posterius" (a), a 

 large opening left between the petrosal, the tympanic bulla, and the basi- and par-occipitals. 

 This gives exit to the jugular vein and the eighth pair of nerves. 



We are unwilling to pull to pieces the skulls of Feiis sjjclcsa, and therefore cannot 

 describe the other three surfaces of the petrosal that are hidden in the perfect 

 crania. A glance at the disarticulated skull of lion or tiger will convey a more ade- 

 quate notion of it in Feiis spelaa than we could convey by the most faithful word- 

 painting. 



Mastoid. — Eirmly soldered to the posterior edge of the petrosal is a massive wedge- 

 shaped-bone (No. 8), the thin end of the wedge passing upwards between the squamous 

 bone and the paroccipitals, and the thick rounded head projecting freely downwards (/). 

 Though cartilaginous in the young Feles, and incompletely ossified even at the age of five 

 months after birth in the lion, it becomes very compact and hard in the adult animal, and 

 perfectly coalesces with the squamosal and petrosal, the suture with the former being a 

 continuation of the lambdoid suture, and rising into a sharp ridge continuous with the 

 occipital crest. In the majority of leonine and tigrine skulls the narrow ascending process 



