6 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



those groups are included which are actually met with or referred to in the manual. For 

 complete classification see the various textbooks, as N, P and H, CNH, etc. Speci- 

 mens of these different groups will be seen in the laboratory in the next section of the 

 manual. 



Phylum Chordata 



Subphylum I. Cephalochordata (Acrania), Amphioxus and its allies. 

 Subphylum II. Urochordata or Tunicata, the tunicates or sea squirts. 

 Subphylum III. Eemichordata (Enteropneusta), Balanoglossus and its allies. 

 Subphylum IV. Vertebrata, all animals with a vertebral column. 



Class i. Cyclostomata, the cyclostomes or round-mouthed fishes, fishlike animals without 



lower jaws or paired fins. 

 Class 2. Pisces, the true fishes, with jaws and paired fins. 



Subclass i. Elasmobranchii, fishes with a cartilaginous skeleton and exposed gill 



slits, including the dogfish, skates, sharks, etc. 

 Subclass 2. Teleostomi, fishes with a more or less bony skeleton and with gill slits 

 concealed under an operculum. 



Order i. Crossopterygii, paired fins with a basal stalk; Polypterus. (See Fig. i.) 



stalk of the fin 



Fig. i. — A, anterior end of a crossopterygian fish {Polypterus) to show the lobe or stalk on which 

 the fin is borne. B, anterior end of a common teleost fish (trout) to show the absence of such a stalk. 

 Tbis difference is not, however, an important distinguishing character between groups of fishes. (From 

 Bridge and Boulenger in the Cambridge Natural- History, courtesy of the Macmillan Company.) 



Order 2. Chondrostei, paired fins without a stalk (Fig. 1), skeleton largely carti- 

 laginous, with a spiral valve in the intestine, heart with a conus arteriosus; 

 the sturgeon (Acipenser) and the spoonbill (Polyodon). 



Order 3. Holostei, like the preceding, but skeleton well ossified; the gar pike 

 (Lepidosteus) and the river dogfish or bowfin {Amid). 

 These three orders are commonly referred to as the ganoid fishes owing to 



the shiny scales (ganoid scales) with which most of them are covered. 



Order 4. Teleostei, paired fins without a stalk, skeleton well ossified, without 

 spiral valve or conus arteriosus; all of the common fishes. This order is 

 commonly referred to as the teleosts or bony fishes. The three orders Chon- 

 drostei, Holostei, and Teleostei are often grouped together as the Actinopterygii 

 or ray-finned fishes in which the fin rays spring directly from the body in 

 contrast to the Crossopterygii or fringe-finned fishes, in which the fin rays 

 spring from a stalk and form a sort of fringe on the end of the stalk. 



