162 ANATOMY OF VERTEBRATES. 



locked with the neural and haemal spines of more advanced 

 vertebrae. 



All these various supports of flaps, fins, or limbs belong to the 

 same natural genetic group of skeletal parts : their peripheral rays 

 are not 'dermal bones;' they are developed between folds, not in 

 the substance, of the integument ; although in some instances 

 they press away the skin and become coated by a ganoid conver- 

 sion or calcification of its outer layer. 



The most simple condition of the parial (pectoral and pelvic) 

 limbs is manifested by the Lepidosiren, fig. 100. A filamentary 

 appendage is sustained by a single many-jointed cartilaginous ray, 

 fio-. 101 a, a. In one species there are attached at right angles 

 to the pectoral ray fine filaments sustaining the narrow fold 

 of membrane continued from its posterior side. A similar series 

 of finer rays supports the membrane continued from the dorsal 

 detached dermoneurals of Pohjpterus. 



Protqptaru8 (Lepidostrcyi) annectejis. xxxin. 



The arch sustaining the pectoral limbs of Lepidosiren is also 

 simple, departing least from its archetypal condition. A long 

 straight cylindrical bone, fig. 101, a, 51, pi, is attached by a short 

 ligamentous mass to the epeneephalic arch, ib. n, of which it is 

 the rib, or ' pleurapophysis,' assuming in ulterior developements 

 the special name of ' scapula.' With each scapula is articulated a 

 larger and more flattened bone, ib. 52 : the two converge and 

 meet at their lower ends, completing, as hamiapophyses, a widely 

 expanded haemal arch. The entire segment, a, conforms to the 

 thoracic modification of the archetype vertebra, fig. 1 9 ; and, simi- 

 larly, is expanded in order to encompass and protect the heart : but 

 it is simplified by the absence of the haemal spine in Protopterus, 

 as the neural spine is sometimes wanting in a neural arch. The 

 haemapophysis, h, in ascending the vertebrate scale, assumes special 

 forms, signified by the term ' coracoid,' with the number 5-2. In 



