108 



THE ANATOMY OF VERTEBRATED ANIMALS. 



oxiiS ; and the Pachycardia, comprising all other Verieorata. 

 The great peculiarities in the development of Amphioxus, 

 and the many analogies with invertebrate animals, particu- 

 larly the Asoidians, which it presents, lend much support to 

 this proposition. 



No fossil form allied to Amphioxus is known. 



II. The MAKSiPOBKANCHn. — In this order of the class 

 Pisces the integument is devoid of scales or bony plates. 



The spinal column consists of a thick persistent notochord 

 enveloped in a sheath, but devoid of vertebral centra. The 

 neural arches and the ribs may be represented by cartilages, 

 and there is a distinct skull presenting cartilage at least in its 

 base, and retaining many of the characters of the foetal cra- 

 nium of the higher Vertebrata. The notochord terminates in 

 a point in the base of this cartilaginous skull behind the pitui- 

 tary body ; and the skull is not movable upon the spinal col- 



f\Q. 80. — A, the skull of a Lamprey, viewed from the side ; B, from above : — a, the ethmovo 

 merine plate; 6, the olfactory capsule ; c, the auditory capsule ; tf, the neural arches of 

 the spinal column; s, the paLitopteiygoid portion ; /, probably, the metapterygoid. or 

 Buperior quadrate, portion, and g, the inferior quadrate portion, of the subocular arch ; A, 

 Btylohyal process; i, ling:ual cartilage; A-, inferior, Hateral. prolongation of the craiiisi 

 cartilage; 1, 2, 8, accessory labial cartilages; m, branchial skeleton. The spaces OD 

 either side oJ 1 are closed by niembrane. 



