MR. ST. GEORGE MIVART ON THE VERTEBRATE SKELETON. 379 
system, but is a median inferior portion of the paraxial system, and is thus a representative 
(and, as far as I know, the only true representative in Fishes) of the sternum. 
4. What is the essential nature, as compared with branchial arches, of the hyoidean arch, 
mandible, and more anterior structures ? 
The hyoid arch and mandible have both been considered by Professor Owen to belong 
to the true endo-skeleton, and therefore to differ radically in their nature from the 
branchial arches, the latter, as has been said, appertaining to the splanchno-skeleton 
according to the same Professor. 
Carus has taken the same view of the hyoidean arch, but not of the mandible. 
Professors Goodsir and Huxley concur in thinking that the mandible and hyoidean 
arches are both endo-skeletal structures, and similar in essential nature to the branchial 
arches behind them. 
I agree in these opinions with the distinguished Professors last named; but, as they 
(as before mentioned) have considered the branchial arches essentially similar to ribs, 
while I do not do so, there is, of course, a similar divergence in our estimation of the 
hyoidean arch and mandible. 
As to structures in front of the mouth, Professors Owen and Goodsir both believe that 
there is a maxillary hzemal arch serially homologous with the mandible; while Professor 
Goodsir counts the palatine arch as a separate hæmal segment. | 
Professor Huxley, in his last Hunterian course, threw out a very original and striking 
idea as to the pree-stomal serial homologues of the mandible. He said*, “ May not the 
maxillo-palatine processes and the trabecule cranii be the most anterior members of 
the same lateral series ? ” 
I am inclined to fully accept this view as regards the trabecule; and I am again 
strengthened, in so doing, by the valuable opinion of my friend Mr. Parker, who has 
described to me the primitive downward-tending position of the trabecule cranii of 
the Frog. 
By an elaborate description of the arrangements of the vascular and nervous systems, 
Professor Huxley supported his conjecture as to the pree-stomal arches, and by the very 
same considerations he seems to me to have conclusively and unanswerably demonstrated 
the essentially similar nature of the hyo-mandibular and branchial arches. He showed 
how the serial homologues of the branchial arteries were represented, or their — 
indicated, by the pseudobranchiæ of Heptanchus and Lepidosiren, and by the * so-called 
carotid gland of the Frog. He stated that the external carotids were the continuations 
forwards of the ventral aortic roots, and that the internal carotids were the representatives 
of the most anterior part of the dorsal aorta. 3t 
He also showed that as the branches of the vagus (Plate LIII. fig. 2,7) skirted the 
branchial arches, so the ninth nerve, or glossopharyngeal, divided and then skirted the 
adjacent sides of the hyoidean and first branchial arches—that similarly the seventh 
nerve divided to go to the adjacent sides of the hyoidean arch and mandible respectively— 
that, in the same way, the fifth nerve supplied the adjacent sides of the mandible and 
* See * British Medical Journal' for June 26, 1869, p. 590. iu 
E 
