It is a surprise to find on surveying the literature
on the development of the mammalian chondrocranium that
though several authors studied the chondrocranium of
various mammals, no attempt has been made to trace system - aticnlly the development of the chondrocranium of Ovis,
specimens of which are so easily available.Under the modern method of investigation adopted in
the present study of the chondrocranium of Ovis the following
conclusions may be drawn. The chondrocranium of Ovis conforms to the generalized mammalian type and could be easily
derived from the reptilian ancestors. Many features
characteristic of placental mammals are clearly exhibited
The following are some of the interesting features which
draw attention.1) The constricted basal plate differs from the wide basal
plate of reptilian origin as in Bos and Equus.2) The presence of the interorbital septum suggests the
the tropibasic skull of reptilian ancestors.4) There is no processus ascendens and the ala temporalis
is a separate cartilage. The presence of an outer bar
of Jacobson's cartilage appears to provide an intermediate
group bridging Archaeorhinata and Caenorhinata.5) There is a definite backward extension of the nasal
capsule.6) The sphenethmoid commissures are slender rods, the
orbito- parietal commissures are broad reminiscent of
amphibian ancestors.7) The chondrocranium of Ovis conforms to the placental
type of chondrocranium.8) The base of the cranium takes a long period to ossify
though a cartilaginous foundation is laid early in the
development.9) The basipresphenoid and the auditory capsules do not
ossify till late in development.10) The Meckel's cartilage takes no part in the formation of
the mandible except to serve as a supporting rod for the
lamellae of the dentary
