328 THE DOG-FISH LESS. 



gelatinous rod, the notochord. The centra, which alternate 

 with the muscle-segments, are connected with a series of 

 cartilaginous arches (N.A), which extend over the cerebro- 

 spinal cavity and with the centra constitute the vertebral 

 column. In the tail there is also a ventral series of arches 

 (ff.A.} enclosing a space (ff. C) which indicates a backward 

 extension of the ccelome in the embryo. 



Anteriorly the vertebral column is continued into a 

 cartilaginous box, the cranium ( Cr) which encloses the brain 

 and the organs of smell and hearing. The jaws, referred to 

 above, are cartilaginous rods which bound the mouth above 

 and below. The gills are supported by a complicated 

 system of cartilages (Br. A, Br. R., Br. R'\ and both 

 median and paired fins by parallel rods of the same 

 material (Ptgpli). All these cartilages are strengthened 

 by a more or less extensive superficial deposit of bony 

 matter. 



The mouth (Mtti) leads into a large oral cavity (Or. cav) 

 which passes insensibly into a wide throat or pharynx (P/i) : 

 from this a short gullet (Gul) leads into a large U-shaped 

 stomach (St), whence is continued a short wide intestine 

 (Int) opening on to the exterior through the intermediation 

 of a small chamber, the cloaca (C!). From the gullet 

 backwards the enteric canal is contained in the ccelome. 

 The greater part of the enteric epithelium is endodermal : 

 only the oral cavity arises from the stomodaeum and the 

 cloaca from the proctodaeum. 



In the skin covering the jaws dermal ossicles of unusual 

 size are developed and constitute the teeth (T). The chief 

 digestive glands are two in number, an immense liver (Lr) 

 occupying the whole anterior and ventral region of the 

 coelome, and a small pancreas (Pn), attached to the anterior 

 end of the intestine. The ducts of both glands open into 



