164 ANATOMY OF VERTEBRATES. 



its pointed upjier extremity j)i'ojects behind that bone and ahnost 

 touches the suprascapula ; a broad angular plate of the coracoid 

 projects backward and gives attachment to the radiated appendage, 

 below which it Ijends inward and forward, gradually decreasing 

 to a point, which is connected by ligament to its fellow, and to 

 the urohyal bone, fig. 43. The inner side of the coracoid is ex- 

 cavated, and its anterior margin folded inward and backward, 

 lodsfins the origin of the great lateral muscle of the trunk. 



In most fishes the lower end of the arch is completed, as in the 

 Cod, by the ligamentous symphysis of the coracoids ; but in the 

 Siluri and Platycephali the coracoids expand below, and are firmly 

 joined together by a dentated suture. In all Fishes they support 

 and defend the heart, and form the frame, or sill, against which 

 the opercular and branchiostegal doors shut in closing the great 

 branchial cavity ; they also give attachment to the ajjoneurotic 

 diaphragm, dividing the pericardial from the abdominal cavity. 



To the inner side of the upper end of the coracoid there is 

 attached, in the Cod and Carp, a bony appendage in the form of 

 a single styliform rib ; but in other Fishes this is more frequently 

 composed of two pieces, as in the Perch. This single or double 

 bone, figs. 34, 38, 85, 58, is slightly expanded at its upper end in 

 the Cod-tribe, where it is attached by ligament to the inner side 

 of the angular process of the coracoid : its slender pointed portion 

 extends downward and backward, and terminates freely in the 

 lateral mass of muscles. In the Batrachii.s its upper extremity 

 rises aljove the coracoid, and is directly attached to the spinous 

 process of the atlas. In some Fishes, as the Snipe-fish ( Centriscus 

 Scolopax), the Cock-fish {Argyrciosus Vomer), the Lancet-fish 

 (^Siganus), it is joined by the lower end to the corresponding- 

 bone of the opposite side, thus completing an independent in- 

 verted arch, behind the scapular one. There is some reason, 

 therefore, for viewing the bone 58 as representing the ha?mal 

 arch of the atlas, or its hiemapophysial portion. 



The usually free lower extremities of these ha;mapophyses, to- 

 gether with their taking no share in the direct support of the pec- 

 toral fins, and their inconstant existence, o]>pose the view of their 

 special homology with the coracoids of higher Vertebrates. 

 To that with the ' clavicles' of higher classes it has been 

 objected that these bones are always situated in those classes in 

 advance of the coracoids ; but this inverted position may be a 

 consequence of the backward displacement of the scapula and 

 coracoid in the air-l)reathing Vertebrates. 



Tlie appendage of the scapular arch, in most Osseous Fishes, 



