186 ON THE MORPHOLOGICAL CONSTITUTION OF 



of the post-stomal sclerotomes are developed each in the cor- 

 responding pair of " visceral laminse," By endeavouring to 

 ascertain, therefore, in which of these post-stomal " visceral 

 laminse" the sclerous elements of the varied forms of the 

 post-stomal hsemal arches are originally formed, the morpho- 

 logical constitution of the individual hsemal arches may 

 reasonably be anticipated. If, again, I am correct in my deter- 

 mination of the constitution of the pre-stomal sclerotomes, the 

 allocation of the individual post-stomal haemal arches to their 

 proper centrums and neural arches follows as a matter of course. 

 From the observations more particularly of Eathke and 

 Eeichert, the formation of the osseous elements of the post- 

 stomal haimal arches in the " visceral laminse," is preceded in 

 each by a more or less distinct and continuous cartilaginous 

 streak or band. Eathke found seven pairs of these cartilagi- 

 nous streaks loosely connected to the basis of the embryo 

 head of the Blennius vivipanis, and corresponding to the man- 

 dibular, hyoidean, first, second, third, and fourth branchial and 

 pharyngeal arches. In the adder the same indefatigable embryo- 

 logist and comparative anatomist foimd a cartilaginous style, 

 with a process directed forward in the position of the maxil- 

 lary, palate, and pterygoid bones, embedded in the first 

 visceral lamina, and its " superior maxillary process," and 

 attached to the side of the basis of the primordial cranium in 

 front of its auditory region ; a similar style lay in the second 

 visceral lamina, and was firmly attached to the base of the 

 cartilaginous cranium behind, and external to the auditory 

 capsule ; a third st}de lay in the third visceral lamina, and 

 was also firmly attached like a rib to the occipital region of 

 the primordial cranium. Similar primordial hiemal arches 

 have been found by Eeichert in the visceral laminse of the 

 mammal and bird, and by numerous observers in the Am- 

 phibia. It is important to observe again at this point, that 

 the relations of all these seven pairs of primordial hsemal 



