344 Mr. W. K. Parker on the Development of the [Feb. 13, 



embryo, it would be close below, and only a little behind, the fore 

 end of the creature ; in this supposed type the notochord would be only 

 a little behind the punctum terminate. 



Now the fore and mid brain have at present only yielded to embryo- 

 logists one pair each of segmental nerves growing from their dorsal 

 region ; the hind brain is a series of enlargements. 



The two great pre-aural segmental nerves (5th and 7th) by the 

 overfolding of the brain, are enabled to send on to the front of the 

 head their special branches, needed there, because of the specialization 

 (for motion) of the third, and the specialization (for sensation) of the 

 first nerve. 



Thus these three-branched nerves have grown in harmony with the 

 paired and unpaired basi-neural cartilages, and there is a due exten- 

 sion forward of cartilages to the partially straightened skull, and a 

 due supply of nerves from behind. 



But in spite of all the metamorphoses of these parts, neural and 

 skeletal, if Dr. Milnes Marshall's observations (with which mine 

 accurately accord) be true, then we still have two true segments in 

 point of the cleft {oral) which is forked over by the 5th nerve. It 

 could not be expected that the visceral arches and intervening clefts 

 would be otherwise than greatly modified and masked in the fore part 

 of the head, with its huge nervous centres, and highly complex organs 

 of special sense. 



The larvae of the Amphibia, especially of the " Anura," have been 

 ^ery carefully studied by me, as likely to throw light upon the order of 

 development of the cranial-facial skeleton ; the lamprey, also repre- 

 senting those larvae permanently, has been the subject of much 

 thought, as a sort of practical pattern of those larvae. In these forms 

 the extra-visceral skeleton of the head is much developed, and only 

 part of the true visceral (internal arches) appear. 



For the mouth in these forms is terminal, and its skeleton is made 

 up of sub-cutaneous cartilages, the serial homologues of the subcu- 

 taneous basket-work of the large respiratory pharynx of the lamprey. 



In that form the only true visceral arches developed are the mandi- 

 bular and the hyoid ; a basal rudiment of the internal branchial arches 

 exists as the " lingual cartilage." 



The free mandible of the lamprey is packed up, and apparently 

 functionless, close behind the postero-superior "labial;" the quad- 

 rate portion of the " suspensorium," is a mere point or style, with no 

 condyle. 



This suspensorium throws a fold of cartilage over the second 

 branch of the 5th nerve and the temporal muscle ; this is not the 

 pterygoid cartilage, and is only seen in this type, in tadpoles, and 

 in some chondrosteous Ganoids, e.g., Planirostra, as shown by 

 Mr. Bridge, 



