OF THE VOMEE, ETHMOID, AND INTEEMAXILLAET BONES. 
313 
If these conclusions are correct, the connexion of the nasals with the intermaxillaries 
and maxillaries behind the nostrils, although so constant, is of altogether secondary 
morphological importance. But it is undeniable that by the great extent of this con- 
nexion in mammals, and by the non-development, in most of them, of any part of the 
intermaxillaries above the septal cartilage, and the separation of the nasals from the 
intermaxillaries in the middle line, where in birds and lizards they come in contact, 
there is a marked attempt, so to speak, on the part of Nature to convert the nasals, inter- 
maxillaries, and maxillaries of the mammal into a neural arch behind the nostrils. This 
tendency reaches its maximum in the human skull, in which the hsemal ring of the 
facial sclerotome has almost, if not altogether, disappeared, and the whole bulk of the 
elements of the haemal arch may be said to be devoted to the formation of what we may 
call the pseudo-arch behind the nostrils. It may be described as an effort to open up 
the closed extremity of the neural cylinder, and at the same time to close the open 
extremity of the haemal cylinder*. 
Still, however, the morphological interpretation of the mammalian nostrils is that 
they are intersegmental clefts. They are similar clefts to those in which the eye and 
ear are developed ; and the alar cartilages pass round the olfactory clefts exactly as the 
tarsal cartilages pass round the optic clefts, and the pinna of the ear and the tympanic 
bone round the auditory clefts. 
Thus these structures are morphologically as well as functionally comparable ; they 
encircle openings which pass from the dermal to the mucous surface, and which prima- 
rily lie in the transverse plane ; although in IMammalia the malar, which belongs to the 
facial segment f, passes backwards and sends up a process behind the orbit, and, in a 
similar manner, the intermaxillary and maxillary send up processes behind the nostril. 
That these processes, however, are not situated so entirely behind the nostril as might 
on first thoughts be supposed, will be perceived if we take into consideration that the 
arch formed by the intermaxillaries and maxillaries lies in the plane of the palate, and 
that processes pointing upwards at right angles to that plane are therefore directed 
ideally backwards. Thus the nasal process of the maxillary is ideally inferior to the 
nostril, in the same way as we have seen that the superior mesial process of the inter- 
maxillary of the bird or lizard is ideally superior to the nostril. 
Let it not be supposed that such a structure as the trunk of the Elephant presents 
any obstacle to the theory of the nostrils here offered. The fusion in the middle line of 
structures undoubtedly lateral in their’ ideal position is well exemplified in cases of sym- 
podia ; and in those monsters in which the head is only developed as far forwards as the 
ears, the pinnae of the ears are united at then’ bases, forming a short tube. 
* If we take into consideration, that the, facial segment is the segment especially engaged in expres- 
sion, I think that I shall not he considered too fanciful in saying that the gradual closing of the haemal 
cylinder and opening of the neural cylinder by the disposition of the bones of the facial segment is in 
harmony with the increasing development of innervation from fishes up to man. 
t This statement, made in passing, is illustrated by the attachment to the maxillaries alone of the largely 
developed malars of the Sloth family and of the vestiges of malars in Myrmecopliaga^ 
MDCCCLXII. 2 U 
