MR. ST. GEORGE MIVART ON THE VERTEBRATE SKELETON. 383 
Goodsir) proves them, in my opinion, to belong to the system of the internal lamin:e, - 
and to be true hypaxial parts. 
Tf, then, my view be correct that the mode of ossification and the degree of segmen- 
tation of skeletal elements is of secondary importance, it seems to me that the subcer- 
vical rings or processes, and the azygos or bifold subthoracie plates of Birds, together 
with their homologues in other Sauropsidans and in Mammals (in fact, all parts in these 
groups which are termed hypapophyses by Professor Owen), are serially homologous with 
the ** chevron bones" of the same animals, and that they all belong to my category A of 
hypaxial parts. At the same time it must always be borne in mind that the hypaxial 
and paraxial parts have a common starting-point, that it is probable à priori that 
they will sometimes coalesce, and that this coalescence may take place before solidi- 
fication, and that thus we may have a skeletal part which is neither completely par- 
axial nor hypaxial, but partakes of the nature of both, and may theretore be called 
parhypaxial. 
The second question about chevron bones has now to be answered, namely, What is 
the nature of the analogous subcaudal arches of Fishes? 
Professor Owen * regards these arches as formed by bent-down paraphyses, i. e. by 
essentially paraxial elements. 1 have not as yet ascertained what precise view Professor 
Goodsir held as to the homology of these piscine arches with parts of the mammalian 
or sauropsidan skeleton. 
J. Müller + considers them to answer to the chevron bones, and the piscine and 
mammalian ribs to be homologous. $ 
A. Müller t thinks the ribs of fishes peculiar, and different from those of mammals ; 
and it seems to follow from his views that “chevron bones" are the homologues of the 
former, the mass of muscles below the lateral intermuscular septum being considered by 
him to answer to the subvertebral muscles placed within the ribs in higher animals. 
- Dr. Cleland $ combats (I think, very successfully) August Müller's view, saying, “ In 
the saurian tail the lateral intermuscular septum is found as in fishes. The muscles 
superior to it are, as August Müller rightly observes, continued into the muscles of the 
back; but the muscles below that line cannot be justly described as continued into the 
interior of the visceral cavity. The superficial ones are attached to the pelvis ; and conti- 
nuous with them, in front of the pelvis, are those muscles of the abdomen which lie 
superficial to the ribs, among others the rectus, which can easily be distinguished in 
some fishes. When the fore part of the tail is laid open, we find, indeed, two masses ol 
muscle continued into the abdominal cavity, and which, as has been shown by Professor 
- Goodsir, are enclosed in the continuation backwards of the lining membrane of the 
abdomen; but that that membrane corresponds not to the lateral intermuscular septum 
of the first, but to the lining membrane of the fish's abdomen, is proved by the co-exist- 
ence of the lateral intermuscular septum, which finds its way to the skin in fishes. For- 
ward in the trunk there are both infracostal and transversi abdominis muscles internal 
| * Anatomy of Vertebrates, vol. i. p. 40. . + Vergleichende Anatomie der MINA, p. 100. 
t “ Beobachtungen zur vergleichenden Anatomie der Wirbelsäule,” Miller's Archiv, 1853, p. 260 &e. 
§ Loc. cit. p. 127. p 
