350 MR. ST. GEORGE MIVART ON THE VERTEBRATE SKELETON. 
palato-quadrate arches, while, finally, the ophthalmie division of the fifth skirted the 
adjacent sides of the palato-quadrate arch and the trabecula cranii of the same side. 
Thus, then, if I am right in believing the branchial arches to be hypaxial skeletal 
elements, it follows that the mandible and hyoidean arches, and most probably the 
trabeculæ cranii are hypaxial also. 
Are there, then, any solid parts belonging to the paraxial kien e. answering to the 
external branchial cartilages of the Elasmobranchs, and to the cartilaginous branchial 
skeleton of the Lamprey (figs. 3 & 4, P)? 
On this point I am not prepared to absolutely affirm any thing; but 1 am inclined to 
believe that the labial cartilages of Sharks (the nature of which has been so much 
disputed) will be found to belong to the paraxial and costal category. Some of the 
complex labial eartilages of the Marsipobranchii may possibly also be of the same nature 
essentially; and it does not seem to be impossible that even some of the cartilages of the 
nose may be modified representatives of the true hæmal arches of the anterior extremity 
of the axial endo-skeleton. 
5. What relation exists between the ** chevron bones” and other parts of the vertebrate 
axial skeleton ? 
By “chevron bones" I mean those subcaudal arches which exist in many Mammals 
and are so largely developed in the Cetacea, and the serial homologues of these arches, 
supposing such homologues to exist. To inquire, therefore, into the relation of these 
bones or processes to other parts of the axial skeleton as it exists in all five classes of 
the vertebrate subkingdom implies the asking of two important questions. 
1. What is the nature of the mammalian “ chevron bones” ? 
2, What is the nature of the analogous subcaudal arches of Fishes ? 
Professor Owen* regards the distinct bony arches beneath the tail of Cetaceans and 
other Mammals, and of Crocodiles and other Reptiles, as the serial homologues of the 
hæmal arches embracing the trunk, while the small arches beneath the cervical vertebræ 
of the Pelican belong, according to him, to another category altogether— namely, to that 
to which the inferior median processes of Serpents and Lizards belong, together with the 
processes to which the chevron bones are sometimes attached, as in Myrmecophaga t. 
In this view of the chevron bone as a hæmal arch removed from its normal costal 
attachment and articulating with the centrum, Professor Owen has not been followed 
by many ; and it is an interpretation I can by no means accept, believing as I do that the 
distinction between autogenous and exogenous parts is of quite subordinate importance?. 
* * Archetype and Homologies,' and Part I. of Memoir on the Megatherium, Phil. Trans. for 1851. 
* See Memoir on the Megatherium, plate liii. fig. 60, Ay. 
+ Dr. Cleland is of a similar opinion, which he thus supports in a passage before referred to :—“ There are caudal 
vertebre in many mammals, the Dog for example, entirely ossified from the centra, which send upwards very small 
pairs of processes forming the rudiments of neuralarches, and outwards small transverse processes. Whatever we 
may think of the latter, we cannot fail to see that there is a greater amount of correspondence between the former 
and neural arches than can be counterbalanced by the fact of their being productions of the centrum and not auto- 
genous.” “So also the anterior part of the upper jaw in man indubitably corresponds to the intermaxillary bone in 
any other mammal, although, except in cases of cleft palate, it is ossified, as M. Em. Rousseau has shown, from the 
