THE LIMITS OF THE CLASS OF FISHES. 79 
obvious ones. All the batrachians have a scapula (in the broadest 
sense) which is homogeneous, the only differentiation being in the 
simple ossification of parts and which is always confined to the 
side; on the other hand, in all the fishes the shoulder girdle has 
somewhat the form of the furcula (wish-bone) of a bird, and really 
forms a girdle behind the head, inclining forward and connected 
below, either by a median cartilage or directly, and a wholly dif- 
ferentiated element (answering to the paraglenal or coracoid * 
region of Batrachians), or elements, support the pectoral member. 
The Dipnoans (Lepidosiren, etc.) and all other fishes agree in this 
respect and differ from the Batrachians. 
In conclusion the following analytical synopsis (extracted from 
the authors “ Arrangement of the Families of Fishes,” published 
by the Smithsonian Institution) will exhibit the principal charac- 
ters which distinguish the several classes confounded under the 
name of Fishes. The characters used are supplemented by many 
others : — 
CLASSES. a 
Skull more or less developed, with the notochord not continued for- 
wards beyond the pituitary body. Brain differentiated and distinctly 
developed. Heart developed and divided at least into an auricle and 
ventricle. 
p 
A. Skull well developed, and with a lower jaw. Paired fins devel- 
oped (sometimes absent through atrophy); and with a shoul- 
der girdle (lyriform or furcula-shaped, curved forwards and 
with its respective sides connected below ł), and with oes 
elements. Gills not purse-shaped. 
B. Skull imperfectly developed and with no lower jaw. Paired 
fins undeveloped, with no shoulder girdle nor pelvic elements. 
Gills purse-shaped. MARSIPOBRAN CHIL 
II. Skull undeveloped, with the notochord persistent and extendin gto 
the anterior end of the head. Brain not distinctly differentiated: 
Heart LEPTOCARDII. 
This is generally ae and its elements have been identified with the radius, 
ulna, and humerus (Owen = third bone of the fore-arm of Cuvier). In a special 
I neie discussed these homologies 
$ i I to be homologous with the 
pu or coracoid elements of the specialized ‘fishes, tl the prose the latter 
ret J 
ea I a ia 3 lt . tat 
preoponaeran 5 I P y reduced. 
