555 
ON SOME DEVELOPMENTS OF THE MAMMALIAN 
PRENASAL CARTILAGE. 
By R. Broom, M.D., CM., B.Sc. 
(Plate xliv.) 
The prenasal element has been shown by Kitchen Parker* to 
be a median cartilaginous development found in the anterior part 
of the head and arising in connection with the front part of the 
cranial trabecule. Though this element is represented in all the 
groups from the Elasmobranchs to Mammals, in the majority of 
forms it is either rudimentary or only found in the young, and in 
the adult it rarely attains any great degree of development. 
In the Elasmobranchs the prenasal cartilage is a well-developed 
structure, and forms the axis of the large rostrum in the Skate 
and other fishes. The rudimentary prenasal found in most higher 
forms is probably an inheritance from these cartilaginous fishes. 
In the bony fishes with the development of the premaxillary 
bones an agent was provided which served the double purpose of 
cutting the water and of giving a firm support for the teeth, and 
the need for the prenasal being thus gone we find it reduced to a 
mere rudiment. 
The premaxillary bones in almost all the higher forms with 
their important tooth-bearing function prevent the development 
of the prenasal cartilage, which though sometimes an element of 
importance in the very young animal, in most cases becomes 
obliterated by the developing premaxillaries. 
In birds the prenasal forms the framework of the beak in the 
early embryo, but as development advances it gradually becomes 
encroached upon by the premaxillaries on either side. In the 
* W. K. Parker. Various Monographs on Development of the Skull, 
Phil. Trans. 
