344 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



liver as an independent and highly specialized organ. This 

 grouj) is named by Plackel the Suhphylum Pachycardia or 

 Craiiiota. 



The numerous forms belonging to the last "subphylum" 

 are again divisible into two great groups. 



In one, the skull has no cincture girdling the mouth, and 

 consequently no lower jaw, there are no pectoral members 

 nor scapular girdle, and there is but one nasal sac, which has 

 a median external aperture. To this section belong the 

 Lampreys and Hags, the rejDresentatives of the class of 

 Marsipohrcmchs. 



In the other, the skull has a cincture surroundino; the 

 mouth, its inferior portion being specialized as a lower jaw; 

 they have (archetypically at least) a pectoral member and a 

 shoulder-girdle developed, and there are two nasal sacs, eacli 

 having ?n olfactory nerve distributed to an external aperture. 

 These Vertebrates are again divisible into three groups or 

 super-classes. 



1. In the first {Lyrifera)^ the shoulder-girdle forms a lyri- 

 form or furcular-shaped apparatus, the scapula and their ad- 

 juncts of both sides being connected together below along 

 the median line, and an air-bladder (sometimes lung-like) is 

 atypically developed (sometimes, however, atrophied), and 



(1) either connects with the oesophagus by a single duct or 



(2) is entirely closed. To this super-class belongs the classes 

 of Fishes and Elasmobranchiates. 



2. In the second (Quadratifera)^ the shoulder-girdle is rep- 

 resented by the scapula? and their appendages, which are 

 limited to the respective sides, a sternum is differentiated, 

 and instead of an air-bladder are two lungs (each with a 

 special canal), which communicate wdth the pharynx. The 

 lower jaw is compound, and is articulated with the skull by 

 the intervention of a special bone the os quadratum. In 

 this super-class belong the Batrachians, the Reptiles, and the 

 Birds ; the last two forming the group Saiiropsida. 



3. In the third {3Ialleifera), the shoulder-girdle is repre- 

 sented by composite scapula?, limited to the sides or back; 

 a sternum is differentiated, respiration is entirely effected 

 by highly specialized lungs communicating with a common 

 trachea, and the lower jaw is composed of simple rami, and 

 articulated directly with the skull, the os quadratum of the 



