114 Transactions. — Zoology. 



on the arch of the atlas. Parotic processes (pterotic + opis- 

 thotic) are not present in their typical form, the post-tem- 

 poral being interposed between these two, and so closely 

 applied as to simulate a cranial bone ; but the opisthotic has 

 a short process, between which and the post-temporal there is 

 a pit for articulation with the supra-clavicle. The lateral 

 border of the pterotic forms eaves overhanging the hyomandi- 

 bular articulation, the surface for which may be traced forward 

 from the pterotic to a pit between the prootic and sphenotic. 



The lower posterior angle of the cranial cavity is a cartilage- 

 lined pit, formed mainly by the opisthotic, between the ex- 

 occipital and the pterotic, and overhung by the epiotic ; it 

 receives the lower end of the posterior semicircular canal 

 which pierces the large epiotic. This bone and its fellow form 

 the upper third of the posterior cranial wall and part of the 

 roof, on both of which they meet by a median suture. The 

 square prootic has its mesial border split longitudinally to form 

 the roof and side-walls of the subcranial cavity for the ocular 

 muscles. This cavity is closed in below by the pai-asphenoid, 

 and extends back into the basioccipital ; the prootics meet 

 behind above this cavity, but in front are separated by the 

 very small prepituitary Y- or rather T-shaped basisphenoid 

 whose slender stem extends downwards between two pro- 

 cesses of the parasphenoid. There is no alisphenoid bone ; 

 and the sphenotic entering into the posterior orbital boundary 

 is almost covered by a lateral-line bone. The frontals are 

 strong curved bones above the orbits, their anterior points 

 flanked by the parethmoids between the orbits and the nasal 

 cavities. The nasal cavities, separated by the supra- ethmoid 

 and the underlying cartilage, communicate with the orbits by 

 foramina between the parethmoids and the median cartilage. 

 Dorsally, between the slender nasals and (between) the 

 lachrymals, above the thin supra- or dermo-ethmoid, there is 

 a long median space in which slide the nasal processes of the 

 premaxillae. The vomer consists of a slender ventral process 

 and two short stout dorsal processes, and embraces the 

 anterior end of the median prenasal cartilage. The lateral or 

 suborbital chain is represented by five bones : first, the large, 

 slightly mobile, fenestrated lachrymals; second, a small bone 

 on the inferior border of the parethmoid ; third, a long bone 

 forming the inferior orbital boundary, having its lower pos- 

 terior angle movably connected with the anterior border of 

 the preopercular ; fourth, a thin plate on the sphenotic ; fifth, 

 a nodular bone in a space between the parietal, pterotic, and 

 post-temporal. 



2. The Jaivs and Sns'pcnsorium. — The short jaws are 

 carried, with the lower end of the hyomandibular, far forward 

 from beneath the cranium ; and the rodlike symplectic, meta- 



