378 



NATURE 



[Feb. 19, 1885 



hedgehog {Erinat -eus europants), as it shows the least suppression 

 of parts, and the best development of that which is diagnostic, 

 so to speak, of the 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 mesopterygoids, and 

 only Jive vomers, yet the anterolateral pair are well developed. 

 Moreover, the tympanic region has only one annulus, the outer 

 bone ; there is no separate os-bullre. Instead of the latterthere 

 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 alisphenold. 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 morphological element as the separate os-bullx, but 

 it has lost its independence. The higher mammalian type is 

 fully reached in the thorough freedom of the alisphenoid from 

 the general cranial wall. This character, indeed, is intensified 

 into the special diagnostic of an insectivore, for it lies almos, 

 wholly outside the orbitosphenoid. Here the sphenoidal fissuret 

 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 

 orbitosphenoid — 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 — 



(1) The development of solid hyaline cartilage in the pterygoid 

 region, a remnant of the pterygo-quadrate of the Ichthyopsida. 



(2) The presence of a persistent pituitary hole, which is con- 

 nected with a curiously specialised structure only seen in typical 

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

 the pituitary region. 



(3) 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 europa>a), 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 character. The nasal 

 labyrinth is relatively immense, and the skull-walls below, later- 

 ally, and behind are as exquisitely pneumatic as in the flying 

 Marsupial (Petaunis), the bird, or the crocodile. The swollen 

 basis cranii, all air galleries within, is so excavated that the 

 hinder sphenoid, both base and wings, largely helps the flat 

 single tympanic to form the drum cavity. The pituitary hole 

 does not exist, but there is a considerable pterygoid cartilage. 

 The ossicula in the adult are normal, but a curious special cha- 

 racter is seen in the ossification, in the young, three parts grown, 

 of the sheath of the stapedial artery, which for a time holds the 

 stapes in its place. It is, however, absorbed afterwards, but 

 remains in the related genus Myogale. In nearly half-grown 

 young moles the malleus is quite like that of the marsupials ; it 

 is an evident " articulare," with copious wild growths of bone, 

 sub-ili tinct, which answer to the "angulare" and "supra- 

 angulare " of a reptile or bird. This malleus in its articular part 

 has two endosteal and one ectosteal bony centre. 



Meckel's cartilage, long continuous with the malleus, is nearly 

 as massive as in the hedgehog, and has a more distinct separate 

 ossification in its sub-distal part, a long, independent, but tem- 

 porary hypobranehial bone. 



The mole shows a most remarkable development of the endo- 

 cranium, which, twenty years ago, suggested to me that its skull 

 retained unmistakable monotrematous characters. In large 

 young of the Echidna and Ornithorhynchus the solidity of the 

 chondrocranium is immense, like that of a Chimccroid Selachian, 

 and the investing bones are thin and splintery. I have not 

 made out the mode of ossification of the inner skull in those 

 types, but in spirit, if not in the letter, the mole agrees with 



them, that is, in the great development and independence 

 of the inner skull. The opisthotic bone ossifies the normal 

 petro-mastoid region, whilst the prootic bony centre begins in 

 its right place on the front edge of the cartilaginous capsule, and 

 then runs away from it into the wall of the skull. Thus there is 

 a large bony tract in the temporal region between the squamosal 

 and the large interparietal, which is not one of the ordinary 

 ectocranial bones, but an endo-cranial bony tract overshadowing 

 and yet imitating the true temporal bone or squamosal. This 

 bone is represented by three separate centres in osseous fishes, 

 namely, the prootic, pterotic, and sphenotic, whilst their true 

 auditory region is partly ossified by the epiotic and opisthotic ; 

 the epiotic is only sub-distinct in the mole. If I am asked why 

 I dive so far down for my illustrations, instead of being satisfied 

 with what reptiles and birds would show me, my answer is thai 

 these are often of no use for comparison, as they are as 

 thoroughly specialised for their own mode of life as the Mam- 

 malia generally, and are as completely, and often more com- 

 pletely, transformed from the original archaic type or types. 

 Thus the mole, likemost of the Edentata lately described by me, 

 suggests as the root stock of the Eutheria generally, not mar- 

 supials (Metatheria), as we know them, but prototherian form's 

 in which, in ages long past, the existing monolremes and mar- 

 supials had a common origin. The shrew (Sorex vulgaris) 

 represents another family of the Insectivores, the Soricidae. It 

 combines the characters of the mole and hedgehog with 

 peculiarities of its own that are manifestly due to dwarfing ; 

 many things are suppressed, as if there was not room in so small 

 a skull for their development. The pituitary hole reappears, 

 and the pterygoid cartilage, but the tympanic wings of the 

 alisphenoid and of the basisphenoid are gone. The malleus 

 does not show itself so unmistakably marsupial, and Meckel's 

 cartilage is slenderer. The sheathing alisphenoids are well seen, 

 the squamosal is extremely small, low down, and devoid of a 

 jugal process ; the jugal bone is suppressed. The prootic wing 

 is present, as in the mole. 



So much for the British representatives of these families of 

 the Insectivora — the Erinaceidas, Talpidce, and Soricidse. The 

 Mascarene Insectivora are so evidently related to each other as 

 to suggest at once a common origin ; these are the Centetidse, 

 the largest of which is the Tenrec (Cenieta ecaudatui) ; the other 

 genera treated of in this paper are ErUulus, Hemicentetes, and 

 Mi rogale. 



These are almost typical Insectivora, but they agree with the 

 shrews in having the jugal bone suppressed ; they are also more 

 marsupial than onr native kinds. In these types the normal 

 characters of the skull of an insectivore are combined with a 

 remarkable marsupial tympanic wing to the alisphenoid, but the 

 os-bullaa is not free, it is merely an outgrowth of bone from the 

 basisphenoid. The pituitary hole is present and in the large 

 species the curious basi-cranial excavation ; the optic foramina 

 also and the sphenoidal side passages are remarkably developed. 

 As in the genus Phalaneista among the marsupials, and Sorex 

 and Talpa among the British Insectivora, the antero-lateral 

 vomers are evidently suppressed, or have a very temporary inde- 

 pendent existence : the postero-lateral vomers are rather small, 

 as in the hedgehog. In the embryo the main vomer is relatively 

 as large as in the embryo whale, and is curiously cellular or 

 spongy. In nestlings this one primary azygous centre has 

 broken up into three : one, the largest, above, and two lesser 

 below, sheathing it, as it sheaths, the base of the nasal septum. 

 Now this multiplication of the vomers proper is thoroughly 

 marsupial. It is unique, as far as I know, in the mode of its 

 sub-division into secondary bony centres. In the African (Con- 

 tinental) family the elephant or jumping shrews (Macroscelidae), 

 as illustrated by the largest forms, Petrodromus and Rhynchocyon, 

 we have a curious mixture of mar-upial or metatherian and 

 eutherian characters, so that they are aberrant as insectivores ; 

 the marsupial characters are most remarkable. These are : 

 (1) the absence of an optic foramen in the embryo ; (2) the 

 alisphenoids scarcely overlapping the orbitosphenoids ; (3) the 

 tympanic wings of the alisphenoids are well marked, hollow 

 shells in the embryo ; (4) large antero-lateral vomers and 

 postero-lateral vomers as large as in average marsupials, and, as 

 in many of them, meeting and uniting at the mid-line ; (5) a 

 large distinct "os-bullce," which makes a tympanic cavity as 

 large as, and much like that of, Petaunis or Phased iretos. On 

 the high eutherian side we have, in the embryo, frontals as large 

 as the parictals, and, strangest of all mammalian specialisation, 

 a long proboscis, composed of thirty double rings of cartilage, a 



