484 



PISCES— FISHES. 



process projects outwards, and bears a minute hint of a 

 rib. From the dorsal surface of each centrum two neural 

 processes arise, and arch upwards for a short distance on 

 each side of the spinal cord. Between each two vertebral 

 there is at each side a broad intemeural plate, which not 

 only fills what would be a gap between the neural processes 



_ ft __i Bi ____ ^„^ and the slightly de- 



• i !, i'l"'\ veloped neural spine, 



but also links the 

 vertebrae together, so 

 that on surface view 

 the segmentation of 

 the vertebral column 

 is far from obvious. 

 In the caudal verte- 

 brae, what seem to 

 be the transverse pro- 

 cesses are directed 

 downwards, to form 

 a haemal arch enclos- 

 ing the caudal artery 

 and vein. In the 

 lozenge-shaped 

 spaces between the 

 vertebras lie gelatin- 

 ous remains of the 

 notochord. The 

 vertebral column de- 

 velops, as usual, from 

 the mesodermic 

 sheath of the endo- 

 dermic notochord. 



The skull is a car- 

 tilaginous case, with 

 a spacious cavity for the brain, a large posterior aperture or 

 foramen magnum through which the spinal cord passes, two 

 condyles working on the end of the vertebral plate, a large ear 

 capsule on each side posteriorly, a similar nasal capsule on 

 each side anteriorly, a long rostrum in front, two fontanelles 

 on the roof. Compared with the skull of a cod or of a higher 

 Vertebrate, that of a skate is simple ; it is not ossified, nor 



Fig. 203. — Under surface of skull and arches 

 of skate'.— After W. K. Parker. 



l.\ First labial cartilage ; R., rostrum; r>., tra- 

 becular region ; n.c, nasal capsule ; a.o., antor- 

 bital cartilage ; p.pt.q.. palato-pterygo-quadrate ; 

 M.c. Meckel's cartilage; k.m., hyo-mandibular ; 

 h.brX- 5 , hypobranchials ; c.br. 5 , fifth cerato- 

 branchial ; c.h., cerato-hyal ; Z. 2 - 4 , labial cartil- 

 ages. 



