688 



COMPARATIVE ANATOMY 



"The cartilaginous visceral skeleton arises in the pharyngeal region 

 which is weakened by the presence of the gill clefts. It consists of a 

 series of pairs of bars, the visceral arches lying in the septa between the 

 clefts, the bars of a pair being connected below the pharynx. Each 

 bar, at first, is a continuous structure, but to allow for changes of size in 

 the pharynx, each becomes divided into separate parts, while the arches 

 become connected in the mid-ventral line by unpaired elements, the 



orbit Uc 7 sule 



chondrocranium \_^ N k hj^andibular *uralardi intercalary arch 



olfactory capsule 



pharyngobranchial 

 epibranchial 

 -ceratobranchial 

 hyobranchial 



basibranchial 

 or copula 



pterygoquadrate 

 cartilage 



mandibular (first) 

 gill arch 



Meckel's 

 cartilage 



hyoid (second) 

 gill arch. 



V.Vl.VIl, of. I'll. 

 \p. n.a, .,/. c. r.r. ^ ^ r. an.c. t.c.J. ! Lo.c. \ of. V. V-- f ^ ^ 



... fw^m^m 







///. hy.a. 



1. 

 Fig. 407. 



I. Diagram of the chondrocranium vertebral column, and gill arches of an 

 elasmobranch to show particularly the parts and relations of the seven gill arches. 

 (Hyman's modification of Vialleton. ) 



II. Skull and part of the backbone of a dogfish, seen from the right side. The 

 skeleton of the visceral arches has been pulled a little downwards, au.c., Auditory 

 capsule ; 6.6., basibranchial cartilage ; b.h., basihyal cartilage ; c., centrum ; cer.h., 

 ceratohyal cartilage ; cer.b., ceratobranchial cartilages ; d.r.,v.r., foramina for the 

 dorsal and ventral roots of a spinal nerve ; e.m., extrabranchial cartilages ; e.c.f., 

 xternal carotid foramen ; ep.b., epibranchial cartilages ; e.l., ethmopalatine liga- 

 nent ; gr., groove for vein which connects orbital and anterior cardinal sinuses ; 

 g.r., gill rays ; hy.a., foramen for hyoidean artery ; hymd., hyomandibular cartilage ; 

 i.o.c., interorbital canal ; i.p., intercalary plate ; M.c., Meckel's cartilage ; I.e., 

 labial cartilages ; nas.c., nasal capsule ; n.a., neural arch ; n.sp., neural spine ; o.n.f., 

 orbitonasal foramen; op.V., opVII., foramina for ophthalmic, branches of fifth 

 and seventh nerves; op'., foramen through which combined ophthalmic nerves 

 pass from the orbit to the snout; op.g., grooves for op.V., VII.; orb., orbit; 

 p.sp.l., postspiracular ligament ; pal.b., palatine bar ; ph.b., pharyngobranchial 

 cartilages; r., rib; rost., rostrum; tr., ^entrilateral (so-called transverse) process. 

 (After Borradaile.) 



