134 



Mr. W. K. Parker. 



[Jan. 29, 



order. In it the great investing bones of the skull are similar to those 

 of the Marsupial, but the nasal and squamosals are smaller, and the 

 frontals are larger. In the hard palate there is a considerable relapse, 

 as in Marsupials ; certain tracts of bone being absorbed, but it has no 

 mesopterjgoids, and only five vomers, yet the anterolateral pair are 

 well developed. Moreover the tympanic region has only one annulus, 

 the outer bone ; there is no separate os-bullse. Instead of the latter 

 there is a crescentic shell of bone, which grows from the basisphenoid, 

 greatly increasing the size of the tympanic cavity. In the endo- 

 skeleton in front of the tympanic cavity there is a remarkable ridge 

 of bone growing outwards from the alisphenoid. That ridge is the 

 remnant of the alisphenoidal tympanic wing of the Marsupial, and the 

 shell of bone growing from the basisphenoid is the same morpho- 

 logical element as the separate os-bullae, but it has lost its indepen- 

 dence. The higher Mammalian type is fully reached in the thorough 

 freedom of the alisphenoid from the general cranial wall. This cha- 

 racter, indeed, is intensified into the special diagnostic of an Insecti- 

 vore, for it lies almost wholly outside the orbitosphenoid. Here the 

 sphenoidal fissure, which in this case lets out the second branch of the 

 fifth, but not the optic nerve — that nerve having its own foramen in 

 the orbito-sphenoid — is not a mere gap, but a side passage, or a sort 

 of sphenoidal corridor, right and left. In these things the Hedgehog 

 is higher than the Marsupial, but in some others it is lower, or more 

 archaic. These latter characters, which suggest an uprise from a 

 more general type than the existing Metatheria, are — 



1st. The development of solid hyaline cartilage in the pterygoid 

 region, a remnant of the ptery go-quadrate of the Ichthyopsida. 



2ndly. The presence of a persistent pituitary hole, which is con- 

 nected with a curiously specialized structure, only seen in typical 

 Insectivores, namely, a hollowing out of the basis cranii beneath the 

 pituitary region. 



3rdly. A third archaic character, not seen in the existing Marsu- 

 pials, is the huge relative size, long persistence, and separate distal 

 ossification of Meckel's cartilage, so that in the embryo Hedgehog, and 

 even in the nestling, the primary lower jaw is as large as in fishes 

 generally, scarcely excepting the Selachians. 



The ossicula auditiis are typically Eutherian ; we have lost the 

 imperforate stapes or columella, the interhyal is very small or absent, 

 and the malleus and incus are much like what we find, in the higher 

 Mammals, generally. The pneumaticity of the skull is much reduced : 

 the olfactory region is almost double the relative size of that of a 

 Marsupial. In the head of another family of the Insectivores, namely, 

 the Mole (Talpa europcea) there is much that is in accord with what 

 is found in its distant relation the Hedgehog, but in it there are 

 evident signs of degradation and of relapse into what is Marsupial in 



