564 



ON THE THEORY OF THE VERTEBRATE SKULL 



their appearance as osseous deposits in the branchiostegal membrane, 

 behind, and on the outer side of, the posterior crus. 



If we turn to the higher Vertebrata, we find, as I have stated 

 above, that, at an early period of their embryonic existence, they also 

 present a cartilaginous arch, stretching from the ethmo-presphenoidal 

 cartilage to the auditory capsule, and supporting the mandibular or 

 Meckelian cartilage on the condyle furnished by its inverted crown. 

 The anterior part of the anterior crus of this arch becomes the 

 palatine bone, which is therefore truly the homologue of the fishes' 



Fig. 8. — Cranium and face of young Gaslei-ostei s.t different ages. Ttie left-hand figure is a 

 view of the base of the skull of a very young fish. The middle figure represents the 

 under aspect, and the right-hand figure, a side view of a longitudinal section, of i more 

 advanced stickleback's skull. 



C Notochord. P. Pituitary space. AC. Auditory capsules. T. Trabecule cranii. E.V. 

 Ethmovomerine cartilage. P. Q. Palatoquadrate arch. Qu. Quadratum. S.Y. or Sy. 

 Symplectic. H. Hyoidean arc. H.M. Hyomandibular cartilage. The other letters 

 have the same signification as in the preceding figures, except ftnx. Premaxilla. mx . 

 Maxilla, d. Dentale. an. Angulare. at. Articulare. Tsik. Meckel's cartilage. 



palatine. The posterior part of it becomes the pterygoid, which 

 therefore is the homologue of the pteiygotdieji (and transversef) of 

 the fish. 



The produced crown of the arch in the higher V ertebrata becomes 

 either the incus, or its equivalent, the quadratum. I therefore 

 entertain no doubt that the jugal is really the homologue of the 

 quadratum of other oviparous Vertebrata. That the tympanal has 

 no relation whatsoever with the bone of the same name in the 



