THE SKULL OF FISHES. 77 



cartilage. The anterior or vomerine part forms a long pyramidal 

 I'ostrum, to which are articulated cartilages connecting its extremities 

 with the radial or anterior angles of the enormously developed hand 

 (pectoral fin) : in the space between the skull and those fins, the 

 Torpedo carries its electric batteries. The tympanic pedicles are 

 short and thick ; the maxillary and mandibular arches long and wide, 

 stretching transversely across the under part of the head. 



In the ordinary Sharks the anterior prolongation of the cranial 

 cavity gives a quite anterior position, and almost vertical plane, to 

 the fontanelle : three columnar rostral cartilages are produced, two 

 from above, and one from between the nasal cavities, which processes 

 converge and coalesce to form the framework of a kind of cut-water, 

 at the fore-part of the skull. In the place of articular condyles, pro- 

 cesses extend backwards from each side of the occipital foramen and 

 clasp, as it were, the bodies of three or four anterior vertebrse of the 

 trunk. The pterygoidean arches extend outwards, in Carcharias, 

 from the base of the cranium, but, as in embryo osseous fishes, are 

 confluent therewith at both ends. The maxillary arch, suspended 

 near its closed anterior extremity to the vomerine part of the base of 

 the skull, is thence extended backwards to the articulation of the 

 lower jaw. A simple cartilaginous pedicle forms the upper part 

 (pleurapophysis) of the mandibular arch, which is completed below 

 by the lower jaw. A few cartilaginous rays diverge outwards and 

 backwards from the pedicle, and support a small opercular flap or 

 fin. The hyoid ai'ch consists of a basi-hyoid and two simple cerato- 

 hyoid cartilages ; the stylo-hyoid is ligamentous, as in the Squatina. 

 Short cartilaginous rays diverge from the cerato-hyoid to support the 

 branchiostegal membrane, or hyoid fin. The scapular arch, which 

 we shall find normally articulated with the occiput in osseous fishes, 

 is attached thereto, at a little distance behind the head, by ligament 

 and muscles in the sharks : from this ai'ch, also, cartilaginous rays 

 immediately diverge for the support of a radiated appendage or fin ; 

 the third in the series counting backwards from the tympanic or 

 opercular fin. 



The capsules of the special organs of sense are all cartilaginous : 

 that of the ear is involved in the lateral walls of the cranium ; that 

 of the eye is articulated by a cartilaginous pedicle with the orbit ; 

 and the olfactory sacs are over-arched by the nasal processes of the 

 epicranial cartilage. 



Amongst the stranger forms in which special development radiates, 

 in diverging from that stage of the common vertebrate route attained 

 by the Plagiostomes, may be noticed the lateral transverse elongations 

 of the orbital processes, supporting the eye-balls at their extremity, 



