COMPARATIVE ANATn.MY. 



the underlying hyaline primordial skull persists entirely v < Vra- 

 todus), or to a large extent. Gill-covers and branchiostegal rays 



Fi<;. 54. CKAMAI. SKKI.KTON. PKCTOK.U. AKCH, AND ANTKIIUUI EXTKKMITY 



Protopterus. 



11', Jf" 1 , the vertehr.e which are fused with tin- skull, with their spinous 



(Psp, Pup 1 ) ; 0<r, supraoecipital, with the hypoglossal foramina ; nh, auditory 

 capsule ; Tr, trabecula, with the foramina for the trigcminal and facial nerves ; 

 FP, fronto-parietal ; ///. membranous fontanullp, perforated by the optic foramen 

 (II) ; /S'A", sujira-orbital ; XE, supra-ethmoid ; .A" A', cartilaginous nasal cajisule ; 

 .IF, antorbital process (the labial raitilai^', which has a similar position and direc- 

 tion, is not indicated) ; PQ, palatoqnadrate, which converges towards its fellow 

 of the other side at 7'V ; ,sv/, squamosal, covering the quadrate ; ~l,A l , articular 

 joined to the hyoid (Hi/) \>y a fibrous band (Ji) ; D, external dentary ; ft, Meckel's 

 cartilage, which is freely exposed, and grows out into prominences ; SL, ena- 

 melled ridge ; ft, b, teeth ; Op, Op } , rudimentary opeivular liones ; / to /'/, tlie 

 six branchial arches ; KR, cranial ribs ; LK, M k'. lateral and median bony lamella', 



which cnslieathe the cartilage of the ] toral arch (A'n, A"//. 1 ) ; co, fibrous band. 



which binds the upper end of the pectoral arch with the skull; X, articular 

 head of the pectoral arch, with which the basal segment (l>) of the five extremity 

 articulates ; *,*, rudimentary lateral rays nf the extremity biscrial type) ; 1, 2, 3, 

 the three next segments of the free extremity. 



ure present, though greatly reduced, and even the five or six car- 

 tilaginous gill-arches are in a very rudimentary condition. The 

 sharp, blade-like teeth, covered with enamel, deserve notice 



Teleostei. In this group, the skull presents a large amount 

 of variation ; its ground-plan, however, may alwavs lie derived from 

 that of the bony Ganoids, and more particularly from Amia 

 calva. On the other hand, no relations with the Amphibia, are 

 observable, and we must, consider the whole group of the IMMIV 

 Fishes as a side branch of the piscine phylum. 



