20 MR. W. K. PARKER ON THE STRUCTURE AND 



cincture. On the outside the quadrate cartilage (7.) sends a process inwards which 

 is tied by a ligament to the corresi^onding trabecular liorn {c.t7\), and thus the circle 

 is completed. From this part the cornua turn downwards in a gentle manner, as they 

 diverge, and end in a broad, sub-emarginate flap. 



The sclerotics and nasal roofs, which were beginning to chondrify, having been 

 removed, we have only the auditory sacs to describe in this stage. 



They are now thoroughly cartilaginous, and quite confluent with the cranial walls, 

 roof, and floor. Moreover, they are swollen with the growth \\'ithin of the three wide 

 canals, and the sacculated base of the membranous labyrinth {a.s.c, h.s.c, 2^.s.c., vh.). 



A crescentic flap of cartilage grows outwards from the horizontal canal ; this is the 

 " tegraen tympani," under that roof we see the large fenestra ovalis, and the well- 

 fitting oval stapes {yh., st.). The fore angle of the tegmen has a flap of cartilage 

 growing from it, the result of coalescence ; this, the rudunentary " annulus," will be 

 described soon. 



Leaving out some of the smaller passages, we may refer to the double passage for 

 the 9th and 10th nerves (fig. 6, IX., X.), the single passage for the 7th and 5th 

 (VII., V.) and the fenestra for the 2nd nerve (II.) : the 8th and 1st are out of sight 

 in this view. 



Each of the huge " mandibular piers " is two-thirds the length and two-thirds the 

 breadth of the ci-anium proper. Besides the two earliest conjugations with the basal 

 cartilage, each bar articidates by its "otic i^rocess" with the cartilage that projects 

 from the tegmen tympani, and is tied, as above stated, near its distal end to the 

 cornu trabecula). 



It is thus swung at four points from the basis-cranii, but of these, the " pedicle " is 

 the true apex or dorsal end (fig. 6, 'pd.), it lies beneath the parting of the facial and 

 trigeminal nerves (VII., V.), and runs parallel for some distance with the ft'ont face of 

 the auditory capsule. 



Between the pedicle and the palato-pterygoid bar there lies a large subocular fenestra 

 (s.o.f.), or membranous space, parallel with the skull ; and behind the pedicle a smaller 

 oblique space is formed, bounded behind by the ear-sac. 



The large " suspensorium " is thick at its outer edge, and thin at its inner, which 

 rises somewhat from its smooth, sinuous, upper face ; on this the long tempoi-al muscle 

 rests, as it passes from its origin in the post-orbital region, to its insertion on the 

 " coronoid " crest of Meckel's cartilage (ml:). 



The suspensorium is terminated by a reniform condyle for the mandible (7., ml:), 

 and opposite the ethmoid it has on its under surface, at the outer edge, a pyriform 

 flattish facet for the hyoid plate {hy.f.). 



Over this secondary condyle, which projects outwards, the suspensorium is developed 

 into a large rounded leaf, with a broad adherent base, a ribbed edge, and a hollow 

 upper surfxce^this is the "orbitar process" (or.p.), which bends over the temporal 

 muscle and is tied by its apex to the skull wall in front. 



