DEVELOPMENT OF THE SKULL IN THE MAMMALTA. 223 
a very perfectly limbate margin, with a flat outer face all round, for insertion into the 
fenestra ovalis. I did not find any interhyal segment. ‘The short round epihyal 
(tig. 2, e.hy.) is followed by membrane up to the equally small hypohyal (fig. 8, A.hy.). 
The basal piece (b.h.br.) is a longish transverse bar, narrow in the middle where it is 
beginning to ossify, and then where it reaches the hypohyals it is thicker ; thence, at 
a very obtuse angle, the thyrohyals (¢.hy.) grow outwards and backwards, without any 
sign of segmentation from the basal piece. 
Third Stage.— Young of Centetes ecaudatus ; 34 teches long. 
I. The investing bones of the skull. 
At this stage, before the development of the crests and ridges seen on the hind 
skull in the adult,* the general form is like that of a Mole, or still more of a Shrew, 
as there are no jugal bones. Very little of the great fontanelle is now visible at the 
junction of the parietals and frontals, and the whole investiture of bony plates is 
strong and smooth; ossification takes place very rapidly in this type, but not so 
rapidly as in the Marsupials, whose premature birth is provided for by precocious 
ossification of the skull. 3ehind the moderately long, and rather slender snout 
(al.n.), the skull is at first narrow, and then widens gently to its orbital ‘‘ waist ;” the 
temporal region is the widest, notwithstanding the great size of the maxillaries with 
their large teeth and tooth-sockets (Plate 33, fig. 1). In the wpper view, we see that 
the nasals (fig. 2, 7.), flanked by the premaxillaries and maxillaries (px., max.), are 
long, and already give promise of the intense ossification of the Tenrec’s skull. 
The notch between the nasals in front is followed by a suture dividing their fore 
third, and behind, there is a slight division ; for the rest they are thoroughly confluent. 
The frontals (f.) are longer than the nasals, but their mutual suture—the frontal—is 
only two-thirds the length of the bones, as the nasals run their double wedge far in 
between them. The frontals, in turn, to a less degree, divide the parietals (p.), and 
their strong suture—the sagittal—is only two-thirds the length of the frontal suture. 
There is a remarkable amount of mutual inter-wedging above, in the preorbital region, 
for the frontals divided by the nasals run forwards between the maxillaries and the nasals, 
whilst the lesser premaxillaries do the same between the nasals and maxillaries, in 
front, so that the latter only reach the middle part of the nasals for a short distance. 
The supraorbital region of the frontal passes very gently down into the orbital, and 
each bone gently widens out to the postorbital corner. From the V-shaped coronal 
suture the parietals widen at first very little, and then suddenly in the temporal 
region; they are bounded behind by the huge interparietal (v.p.), and divided from 
it by the lambdoidal suture. 
The suture is, here, an inverted \/, and is similar to the coronal; its crura are 
coneave in front, those of the coronal are arched forwards. The dentation of these 
* See Dorson’s “ Insectivora,” Part ii., Plate 8, figs. 1, La. 
