80 DEVELOPMENT OF THE SKELETON OF THE TUATARA. 



PLATE III. 

 SpHENODON PUNCTATUS. — DEVELOPING SKULL, EARLIER STAGES. 



The figures on this Plate are of wax models reconstructed from microscopic sections, 

 the skeletal parts being alone represented. The fenestrse and interspaces in the 

 chondrocranium are for the most part occupied by membrane (not indicated), except 

 in so far as they transmit nerves and blood-vessels (c/. PL IV. fig. 10). 



an., angular ; ar., articular ; b.s.', basipterygoid process ; cJ, auterioi- semicircular caual ; 

 c.aiL, auditory capsule; c.r., coronoid ; d., dentary ; ex., extrastapedial cartilage; e.«., external 

 nares ; e.o., exoccipital; epg., epipterygoid ; e.s., etlimosphenoidal plate; ex., extranasnl; ex.^~*, 

 extranasal processes ; /. i.-xii., foramina for exit of cranial nerves ; f.a., foramen for oplithalmic 

 branch of the carotid; f.e., ethmoidal foramen; f.L, interorbital fenestra; f.j., foramen for jugular 

 vein; /.m., foramen magnum ; /.»., lateral cranial fenestra ; /r., frontal; h., hyoid ; h.', anterior 

 cornu of the hyoid ; h." , posterior cornu of the hyoid; i.n., iuternal nares ; _/., jugal ; mk., Meckel's 

 cartilage; Wia?., maxilla ; wi.t'.'^ maxdlary process; «. a.;?. , alinasal process ; wc, notochord ; w.c, nasal 

 capsule; n.c.', supranasal process; n.c", prenasal i^rocess ; n.f.', nasal fenestra; n.pa.p., naso- 

 palatine process; n.p.p., naso-premaxillary process; ns., nasal; n.v.p., inferior naso-vomerine 

 process ; oc.c, occipital condyle ; os., otosphenoidal plate ; 05.^"', otosphenoidal processes ; 

 p., parietal ; pa., palatine ; par., parachordal ; p.f., prefrontal ; pg., pterygoid ; pg.' , pterygoid 

 process; p.o., postorbital ; po.f., postfrontal ; p.p., parotic process; pq., pterygo-quadrate : 

 ps., presphenoidal cartilage; p.-^., parasphenoid ; px., premaxilla ; py.', pituitary foramen; 

 5'., quadrate; 9.', otic process of quadrate; g^'., quadrato-jugal ; 5.a., supra-angular; «6., subnasal ; 

 S.I., interorbital septum ; s.mx., septo-maxillary ; s.o.', supraoccipital cartilage ; sp., splenial ; 

 sq., squamosal ; sq.'', posterior process of squamosal ; s.st., suprastapedial cartilage ; St., stapes ; 

 t.p., transpalatine ; tr., trabecula ; vo., vomer. 



Fig. 1 '. Stage P. Developing chondrocranium : — Left lateral aspect. The arrow indicates the 

 direction of the longitudinal axis of the embryo as it lay coiled. 



Stage P. The same : — Ethmoidal, trabecular, and sphenoidal regions, dorsal aspect. 



Stage P. The same : — -Parachordal and auditory regions, dorsal aspect. 



Stage Q. Developing chondrocranium : — Lateral aspect. 



Stage Q. Developing skull : — Lateral aspect. 



Stage Q. Developing chondrocranium : — Ventral aspect. 



Stage Q. The same : — Dorsal aspect. 



Stage R. Developing chondrocranium : — Lateral aspect. 



Stage R. Developing skull : — Posterior aspect. 



Stage R. The same : — Lateral aspect. 



Stage R. The same : — Doi'sal aspect. 



Stage R. The same : — Ventral aspect. 



' In these figures the uncoloured areas represent pro-cartilage. 



Fig. 



2\ 



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10. 



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]1. 



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12. 



X 1.3. 



X 1.3. 



X 13. 



X 8. 



X 8. 



X 8. 



X 8. 



X 8. 



X 8. 



X 8. 



X 8. 



X 8. 



