CHAPTER XX. 



THE PECTORAL AND PELVIC GIRDLES AND THE 

 SKELETON OF THE LIMBS. 



The Pectoral girdle. 



Pisces. Amongst Fishes the pectoral girdle presents itself in its 

 simplest form in Elasmobrauchii, where it consists of a bent band 

 of cartilage on each side of the body, of somewhat variable form, 

 meeting and generally uniting with its fellow ventrally. Its anterior 

 border is in close proximity with the last visceral arch, and a trans- 

 verse ridge on its outer and posterior border, forming the articular 

 surface for the skeleton of the limb, divides it into a dorsal part, 

 which may be called the scapula, and a ventral part which may be 

 Called the coracoid. 



In all the remaining groups of Fishes there is added to the car- 

 tilaginous band, which may wholly or partially ossify, an osseous 

 support composed of a series of membrane bones. 



In the types with such membrane bones the cartilaginous parts 

 do not continue to meet ventrally, except in the Dipnoi where there 

 is a ventral piece of cartilage, distinct from that bearing the articu- 

 lation of the limb. The cartilage is moreover produced into two 

 ventral processes, an anterior and a posterior, below the articulation 

 of the limb ; which may be called, in accordance with Gegenbaur's 

 nomenclature, the pra^coracoid and coracoid. Of these the pree- 

 coracoid is far the most prominent, and in the majority of cases the 

 coracoid can hardly be recognised. The coracoid process is however 

 well developed in the Selachioid Ganoids, and the Siluroid Teleostei. 

 In Teleostei the scapular region often ossifies in two parts, the smaller 

 of which is named by Parker pra^coracoid, though it is quite distinct 

 from Gegenbaur's praecoracoid. The membrane bones, as they pre- 

 sent themselves in their most primitive state in Acipenser and the 

 Siluroids, are dermal scutes embracing the anterior edge of the car- 

 tilaginous girdle. In Acipenser there are three scutes on each side. 

 A dorsal scute known as the supra-clavicle, connected above Avith 

 the skull by the post-temporal; a middle piece or clavicle, and a 



