58 



EVOLUTION AND GENETICS 



Fig. 35. — Diagram of an early elasmobranch chondrocranium in side view; 

 the brain outlined, al, alisphenoid plate; bp, basal plate; gc, gill clefts; 

 h, hyoid; hm, hyomandibular; /, upper labials; U, lower labials; ?n, Meckel's 

 cartilage; nc, nasal capsule; oc, otic capsule; oi>, occipital vertebrae; ptgq, 

 pterygoquadrate; si, suspensory ligaments; sp, spiracle; tr, trabeculae; v, 

 vertel)rae; I-VII, visceral arches; 1-5, branchial arches. (From Kingsley's 

 Comparative Anatomy of Vertebrates, with the permission of P. Blakiston's 

 Son & Co.) 



Fig. 36. — Dorsal (A) and ventral (B) views of the skull of Cryptobranchus 

 allegheniensis, a primitive salamander. Dermal bones: PMX, premaxil- 

 lary; MX, maxillary; N, na.sal; F, frontal; PrF, prefrontal; P, parietal; 

 Sq, squamosal; Pt, pterygoid; VP, vomero-palatine; PB, paraliasal. Carti- 

 lage bones: OS, orbit osphenoid; Q, quadrate; ExO, exoccipital; Op, opercu- 

 lum. Other parts: Col, columella; Nas, nasal capsules; ec, eye capsule; ot, 

 otic capsule. In both figures the dermal bones are removed from the left 

 half. (From Wilder's History of the Human Body, with the permission of 

 Mrs. H. H. Wilder and Henry Holt and Company.) 



