ii6 



VERTEBRATE SKELETON 



The pterygoquadrate is now firmly united with the cranium by three proc- 

 esses — otic to the capsule, palatobasal to the trabecula and ascending (epiptery- 

 goid) to the sphenolateral region, conditions strikingly like those in Urodeles. 

 The ventral end of the quadrate region articulates with the Meckelian, and a 

 process on the hinder side of the quadrate connects with the hyoid arch, a small 

 cartilage (interpreted by Sewertzoflf as hyomandibula, fig. 122, B) being con- 

 nected with both otic process and otic capsule (Huxley found a hyomandibula. 

 Pollard's opercular cartilage, in the same position in the adult). There were 

 four branchial arches in this stage, the fifth appearing a little later, each with a 

 small epibranchial and a larger ceratobranchial. There is no copula, but the 

 adult has a long one connecting the basihyal with the first ceratobranchial. 

 There is none in other Dipnoan genera. 



The cartilage skull is little ossified in the adult, scarcely more than 

 in Chondrostei. There is a pair of exoccipitals, and in the visceral 



Fig. 122. — Skull of Lepidosiren (Bridge), an, angulare; ap. antorbital process; 

 ch, ceratohyal; cr, cranial rib; de, dermal ethmoid (?supraethmoid) ; dee, dermal ecteth- 

 moid; eo, exoccipital; fp, fronto-parietal; hr, 'hyoidean rib;' mk, Meckel's cartilage; 

 na, first neural arch; nc, nasal capsule; nsp, neural spine; pq, pterygoquadrate; sc, 

 sagittal crest of fronto-parietal; sp, splenial; sq, squamosal 2-10, nerve exits. 



arches only the ceratohyals ossify. The membrane bones are more 

 numerous, but far fewer than in most fossil relatives or in other fishes, 

 and there is no httle difficulty in tracing homologies of many of those 

 present. Overlying the middle of the ethmoid region is a median 

 bone called both dermethmoid and nasal. This is followed by a 

 second unpaired bone, long and slender in Protopterus, wider in 



