36 



ANATOMY OF VERTEBRATES. 



than the neural arches ; nor are interneural and interhaemal pieces 

 wanting. In Raia clavata these ( ossa intercalaria ' constitute the 



chief part of the neural arch, at the 

 anterior part of the vertebral column ; 

 whilst the neurapophyses resume 

 their ordinary share in its formation 

 at the posterior part of the column. 

 In Zygcena there are interspinal 

 cartilages. In Rhinobatus a single 

 spine answers to two vertebral bodies, 

 and we may well suppose this mul- 

 tiplication of central pieces to have 

 been carried still farther in the pri- 

 maeval fossil Ray (Spinachorhinus) 

 from the lower Lias. 



In the anchylosed cervical verte- 

 brae of the Skate the short centrums 

 are indicated by transverse bars along 

 the middle of the under part. In 

 the Monk-fish (^Squatina) the body 

 of the atlas is confluent with the 

 basioccipital, but the neural arch re- 

 mains distinct. 



The parapophyses in most Rays 

 pass forward, and then backward, the 

 angle of one fitting, like an articular 

 process, into the notch of the para- 

 pophysis in advance : they do not 

 support pleurapophyses ; they gradu- 

 ally bend down behind the pelvic 

 arch, and complete the haemal canal 

 about six vertebra? beyond it; the 

 ha3inal spines become flattened in the 

 tail of some Rays. 

 In osseous fishes a trunk-vertebra consists of a biconcave body, 

 fig. 27, c, of a pair of neurapophyses, fig. 31, n, usually develop- 

 ing a spine, ib. ns, from their point of coalescence above the 

 neural canal ; and of a pair of parapophyses, ib. p ; to which 

 are added in the abdominal region in most fishes, and also in the 

 caudal region of some, a pair of pleurapophyses^ pi, figs. 31, 32. 

 Ossification usually commences in the bases of the neur- and 

 par-apophyses, and in the terminal cones of the centrum ; it 

 may proceed to blend the six points into one bone, and fill 



Forepart of skeleton, Piked Dog-fish 

 (Acanthias}. XLIII. 



