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22 



the basioccipital articulating surface, we find a narrow, deep groove (gr) for arti- 

 culation with the articulating process of the first vertebra. On the posterior sur- 

 face of the skull in A. strigata are very deep hollows, much deeper than in scutata; 

 the exoccipitals especially, with the adjoining parts of the postteniporals, have deep 

 hollows surrounded by sharp margins. 



The under surface of the skull (fig. 12) most posteriorly is 

 flattened, but soon becomes angular; at * the parasphenoid (pa) 

 forms a blunt angle in its forward slope; under the orbit it is 

 broader and hollowed out below. The most conspicuous and 

 remarkable bone in the skull is the pterotic (sq); this is joined 

 below by a suture to the basioccipital (ob) and thus shuts out 

 the exoccipital from contact with the prootic. The anterior sur- 

 face of the prootic (pro) bounds the lower part of the cranial 

 cavity towards the orbits and by means of a short horizontal 

 process meets with the corresponding bone of the other side in a 

 medial suture; a fairly deep space is bounded 

 above in this way and below and laterally it 

 is enclosed by the parasphenoid. The recti 

 inferiores muscles of the eye are attached in 

 this, i. e. Amphisile has a distinct indication of 

 a "myodome"; it is however not continued far 

 back like a true "eye-muscle canal", as is the 

 case in Centriscus (cf. later under this species); 

 apart from this the conditions are the same in 

 both species. A small alisphenoid and pro- 

 bably a small orbitosphenoid are present as 

 in Centriscus. Under the broadened, concave part of the orbital 

 portion of the parasphenoid lies the posterior, finely pointed end 

 of the vomer (i>o)\ slightly in front of the prefrontals (prf) — 

 where the cartilaginous portion of these passes over into the 

 mesethmoid — the vomer increases greatly in breadth, and from 

 there, accompanied in the beginning by the cartilaginous meseth- 

 moid, later alone, forms the beak-like anterior part of the skull. 

 The under surface of the vomer is channelled; the lateral edges 

 are (somewhat) thickened; along these edges are attached the 

 mandibular suspensorium, whilst the concave lateral surfaces 

 above the margins are covered by the nasals. Under the broad 

 posterior part of the antorbital bone (ao) lies the anterior portion 

 of the preopercular muscle (M. adductor mandibules) and the long, 

 thin tendon of this muscle is covered by the remaining lower, very thin and trans- 

 parent edge which extends slightly out over the edge of the vomer; the anterior 

 end of the tendon, almost right to its attachment to the upper and under jaw, is 



Fig. II. 

 Amphisile strigiila. Poste- 

 rior surface of llie skull. 

 Leiters as in Hg. 10. gr: 

 articulating grooves on 

 exoccipitals for articula- 

 tion with 1st vertebra. 



] 



s. 



pi 



I'i 



Fig. 12. 



Amphisile sciitatti. 



Skull seen from l>('lo\> 



/)« : parasphenoid; oh 



l)asioceipital; pro: 



prootic. Other letter 

 as in fifrs. 10 and 11. 



